Video shows him getting shot then turning and going back into the store.
The BG seems to take on the body language of "what are you gonna do with that gun?"
I am not saying that deadly force is justified in every incidence that someone is pushed to the ground, but this was a big guy who charged at him and pushed him violently to the ground. Considering the age and size difference, I can clearly see, in this instance, that he felt in danger for his life.