He probably bought a couple of gloves for weapon damage.

ex. Slayer's Wraps: +30 weapon damage, +10 HPS, 10% chance for 2x critical strike 

Angelic Fury IV adds 100 damage per shot (and splash damage). skill info here: http://demigod.wikia.com/wiki/Angelic_Fury

Regulus base damage is 120-135 and he gains +8 per level. so at level 11 his base damage range should be 208 - 223. add in the Angelic Fury damage and its 308-323. even just one item like Slayer Wraps for +30 would get his damage range into the 350s. 

next we have to look at how the Armor stat comes into play. 

Banded Mail and Unbreakable Boots add to health pool but not to armor. you'll still be stuck at Regulus very low base armor level, about 560 armor for a level 10 Regulus. 

the armor equation is this: 100 x (1 - (2500 / (2500 + Armor)))

so 560 armor gives 18% mitigation. this would suggest that actually your opponent's damage was more like 430 before damage reduction, so he probably had an artifact already. 

to explain your damage to him just do the process in the other direction. your base damage at level 10 would have been 200-215 damage, plus 40 from Mard's hammer takes it to 240-265. if he also had about the same armor level as you (approximately 18%) then he would be taking 190ish damage from most of your shots, which is what you saw. 

so basically your opponent had earned alot more money than you and thus bought some high end gear. he was benefitting from at least +110 weapon damage from his items, which is a large amount. a high end artifact like Ashkandor can give that all by itself. lower end items can give it to. Mard's Hammer + Mageslayer + Slayer Wraps will do it.

Add Blade of the Serpent and the Stats upgrades for another 55 damage.  You start getting pretty close.

Demigoddb.com doesnt show damage from abilities, the site is still new, but it does do it from gear and levels.

I set up a level 11 Regulus with (for his level) maxxed out AF and Stats, blade of the serpent, and slayers wraps.

So it shows me that with that gear his damage is 255-281.

Add in AF: 355-381

Add in Stats: 380-411

And this is just with one item bought.  He did this without artifacts.

Eobet,

note: math incoming, if you just want the results and applications to gameplay skip to bottom.

Armor can be complicated to understand unless you get into the mathematics of it and also consider what types of damage you are most likely to receive in any given encounter.

not sure how much math you know, but if you wanted to look at it from this perspective you'll see that the armor equation is of the type: (1-1/x). this is an inverse exponential function. its integral is ln(x). if you graph this kind of function it looks like this:

so on that chart imagine that the y axis is % mitigation and the x-axis is armor value. imagine that the 1 armor value 0.

so if you don't know how this kind of function works you'd think that there's a strong diminishing returns on it because it looks like the curve is flattening out as your armor values are increasing. however, you need to understand that each additional point of armor is compounded on top of existing armor values. so if you graph a different quantity on y you get a very revealing result. imagine that instead of graphing % mitigation you're graphing "time to live" which is a value in seconds learned by dividing your current health by your incoming dps suffered. this is the inverse quantity of %mitigation, i believe. 

the graph would change and look like a straight line plot, like this

so you can tell from this that armor has a linear, non-diminishing increase in the quantity "time to live". the inverse (1/x) of time to live is "% mitigation" which is why you get a graph of ln(x) if you graph the inverse of the quantity you really care about. 

anyway, my apologies for being pedantic and nerdy. i hope the math helps you understand the way armor really works. 

as far as this applies to what items should you buy in Demigod, think of it like this:

1) there's a synergistic relationship between health and armor. armor makes each point of health a "bigger" point. increasing just health or just armor is less effective than increasing both in some proportion. the exact proportion you choose should be related to what your most likely damage sources are.

2) armor does not reduce damage from spells. it reduces damage from everything else though. its a fantastic investment against auto-attack based damage dealers like Angelic Fury Regulus or any Minion build of a General. its much less good against a Mines based Regulus or a DG like Torchbearer that has alot of spell nuke damage. 

3) survivability upgrades are always extremely worthwhile. i highly recommend maintaining a good amount of +health, +armor, and +health regen throughout the entire game. i find that people undervalue Armor because perhaps they don't understand how it really works. 

Pickup nimoth instead of unbreakable and cheap gloves. Get boots of speed or unbreakable later. I find most builds really only need nimoth for going against other heavy autoattackers. Probably start with scaled helm, banded armor, then cheap gloves followed by vlemish helm and or nimoth/unbreakable. It all depends on play style and who you are up against.

On my TB I will usually go anhklet and Scaled with banded. Then vlemish and boots of speed. Then nimoth if im fighting against reg or rook. If not Ill grab wand of speed then save for HoL. Farm a few people and buy giants.

When I play reg I go for speed and dps only and skip snipe.  Forget trying to armour up as regulus, you want to get dps so you can force your opponent to flee otherwise you are just a very rubbish tank with terrible dps.

I usually go:

+15% movement favour

+5 mps hat

+5 hps armour

boots of speed

mageslayer

Then you can just go for more dps items.  Skill wise I prioritize:

max mark of the betrayer

max mines

max range level 3

slow level 1

max angelic

You will just be harassing at the start with auto-attack, with slow and 2 ranks of range you can stay out of damage range from most classes (pounce/vomit etc) and spam betrayer.  You should focus on not dying though and getting gold/xp.

Once you have the gold for mageslayer (after boots obviously) you should have all your core skills and just be pumping angelic.  At that point you can start to slaughter players with your sweet dps.  Ideally you get your team mates to buy the gold upgrades at keep since you really need your items where as classes like QoT, Rook, Sedna etc are far less item based and should be selflessly buying such boosts.

You should try and always carry a universal gadget on you too since it makes up for skipping snipe at the start and is also handy for heals if you catch a couple of vomits/blizzards.