Everyone breaks on the internet at some point. He doesn't do this every day, and he has no history of it, to my knowledge. He just snapped.
All he needed was someone to listen to him, I'm sure. Kicking him out of a game he plays and away from the people he has played with for over a year is very drastic. How many posts did this guy even have? He has barely 50 posts, most of which were from this incident, so he isn't even active in the forums. If he can't control himself in the forums, then take that away from him, not the entire game. He acts perfectly fine in the game for the most part.