Normally I would agree with you but not on this. If that was your boy & a grown ass man put his hands on him for him doing exactly what the kid in the vid did, would you be ok with that? The father had every right to be angry, but to put his hands on another person's child/nephew/grandson over that in public is too much. He's the adult in the situation & that could've escalated real quick because of his out of control emotions. And if the kid retaliated after getting slapped, could you really blame him?
The father could've put the fear of God in the kid w/o putting his hands on him which could still turn ugly because if that kid was related to me, Pop's would have a major problem on his hands