It means either a bug in the game or a hacker.  This early on in the lifetime of the game a hacker seems unlikely.  Also, people generaly don't create non-information hacks/cheats in games like this because of the desync it causes.

It happens when one of the computers in game says one thing happened in the game and one of the others says something different since its p2p there is no real way to correct this.

I got the same thing tonight, and also, every DG game I try to play online today has unusual stuttering* and people dropping out at strange times (i.e. it doesn't look like they dropped on purpose, no reason no warning).

*Is stuttering the same thing as lag?

I ran into this a couple times and it's always cropped up when someone gets disconnected. Assume this means that they were connected to that player but aren't really to everyone else or at least not well which means that their client shows something different than on yours and boom you have it.