Freddy is right.Why are folks quick to bring up a person who didn't have weapons as if this makes them less of a threat, in the real world there is no way for a person who is under attack to properly conclude the attacker's intentions or whether or not he was armed or not.
When it comes to self-defense the biggest factor is whether or not the guy under attack felt like his life was in danger, and according to that video I, and most people, can see why he felt endangered by that idiot.
You cannot assume "force" may be used.
You can only meet force with equal force.
The only other factor was that that dude came around the counter. If he broke into that area then that's probably a crime committed as trespassing.
This is a business. If that dude presented a weapon and you defended your life then OK. But pushing him and fighting him with no weapon, he gonna have an uphill battle.