I don't think there is a problem questioning the number of shots, or questioning that last shot. I would hope that, if I were in that situation, I would be able to know when to stop shooting. In my opinion, he definitely could have stopped shooting once he saw that the guy no longer had the gun in his possession. But, I also can't imagine what it's like to really be in that situation. I guess I would choose to give the benefit of the doubt to the guy who was being robbed, not to the robber. I am also a little concerned about him leaving the scene. If I remember my CCL training, in that situation we should call our lawyer, the cops, and an ambulance. Then we sit and wait for the cops to show up. But I don't know if that's a legal requirement or just something that is recommended.
I saw a longer video that shows that, after the shooting, the guy realizes that the bad guy didn't even have a real gun. He ends up throwing it across the restaurant in anger. For some reason, that was encouraging to me. He wasn't excited or happy about killing a criminal. He was angry about the whole situation.