I have worked for my share of assholes in the past. One in particular was such an unprofessional jerkoff that I still hope I don't ever run into him after I've had a couple of drinks somewhere, because I'd probably be very tempted to at least tell him what I thought of him.
But working for a jerk doesn't give anyone the right to assault someone like that. The kid should have just walked off the job or at least walked away or whatever and talked to higher ups in the company if he was having issues with the manager. I think it's quite likely that the kid has a history of failing at jobs and displaying such irrational and violent behavior to have blown up, played the race card, and punched someone like that over what appeared to be a very minor issue.