Maybe because the guy was with his family.
Looking straight in the eyes at a predator is seen by the predator as a challenge. He didn’t want to give the predator as reason for start throwing fists or worse.
Now if he was alone or the guy hit his child, different matter.
He clearly had more control than I would have exhibited. Call me impetuous, but I’ve had enough and will not suffer this type of thing in front of my wife and kid. I wouldn’t start anything by as I said...one touch.