Probably because he realised he could seriously harm that kid and took the high road. The kid was incredibly lucky, and foolish to hit someone who would've been justified in mopping the floor with him.
He grew up and realized that fighting wasn't the answer. Or maybe he was afraid of harming the other that hit him . Thing is he probably did the right thing.
Because he was about 4 years older than the child, and he is mature enough to know the right thing to do.
what would you have him do....... beat the crap out of a smaller kid --I think he was being the bigger person here, good for him.
Maybe he has some self control. Not punching people is a good thing.