Actually, that would make the most sense. I have seen many African American Apes grab their children and hit their children and talk to their children in very abusive manners and in public! It wouldn't surprise me if that was the case.
There's two general responses to violence if you can't hurt your attacker directly. Some people take it out on others and others turn it in on themselves. Little boys like that tend to act out rather than turn the rage inside at themselves. He obviously needs to be kept away from smaller kids but at the same time I hope he also gets the help he needs. It's not pre-determined that he's going to be a future murderer if he can get help and get away from the situation that's building up that rage.
There might not even be abuse here, it's just a likely possibility.
It might also be he's chemically unbalanced somehow, but no matter what it is he needs to be evaluated.