Why do some people look behind them both ways after unloading their gun at a target?
Judging from the fact that he only fired 6 shots and his slide didn't lock back, I would guess that his gun WASN'T unloaded.
If it was a real situation and you had just fired 6 shots at someone, what would you consider appropriate? Stand there without looking and hope his buddies weren't coming at you from one side or the other?
As others have stated, it's a standard technique taught in any basic self-defense handgun class. Training like you will fight has been proven to be effective for many years.