Guys, guys! Before we shout HaXXoR and Burn the WITCH, lets think this through first. Demigod has a few very powerful tools in place to make this kind of cheating almost impossible. If you edit the blueprints the game will desync, even over Game Ranger. And you can't get online on Impulse with an edited game version at all afaik.
badcad, when something like this happens or you have a doubt, save the replay! You can find it in My Documents\My Games\...\Replays\<Username>\LastGame. While we dont have a working replay system yet, there is a lot of data in those files that is extremely valuable. And there are workarounds to watch them.
My guess is that he may have used unusual settings for the game as Zechnophobe suggested, maybe there was a glitch or something. We don't know yet. Keep an eye out for strange stuff like that, collect information. For the Allfathers sake, don't post usernames unless you are absolutely certain that he used cheats. And by that I mean you have proof.
If you have a replay and there was bugusing, cheating or exploiting, tell a GPG or Stardock employee and send them the replay. They will check it out, ban the user account (if he was cheating) and fix the problem (if there is one).