While I defer to your expertise, I have to say I find it a bit difficult to believe. Being in an online game just changes the form of interaction between people, not the fact that they're interacting. (We couldn't, for example, say "Oh, X is a jerk over the telephone but s/he's not like that in person at all".) These players know full well that there was another human being at the other end of their misbehavior.

Whatever the online analogue of "in vino, veritas" might be, I would be willing to bet that it's true and that these players are actually revealing a significant aspect of their true nature.