I had to rewatch the video a couple times. It really wasn't a sneak at all.
Dude punched his hat off the guys head and then was posturing saying "Swing! Swing!"
Then he decided he didn't want to fight anymore and started talking dude to go away and that he started it.
You can read the old guys body language and see he wasn't done. Evident by him continuing to walk up on him.
I've seen this quite a few times, especially in school. Kid gets one good punch off then before the other kid can get his get back its "

chill, chill, chill! Im done, I'm done!"
Like nah, you not about to hit me one good time then call off the fight.
Dude didn't really want to fight or maybe hurt the old guy but had to defend himself and tried to do the right thing by calling it off, but he stopped analyzing the situation that was in progress.
Just because you are done fighting doesn't mean we are done fighting.
He should've just walked away after he knocked off the dudes cap instead of trying to talk to him.