So, that happened in that confined area with multiple movie cameras shooting it from different angles yet nobody caught it? And notice that you're see the kick there; the muzzle is high. And notice also that he looks steeled there, meaning that his arms are lengthened, and he's using two hands. He's done all he can to control the weapon. But, Ruby only used one hand, and he didn't have the stabilizing effect of being steeled and planted the way this guy was. It seems like Ruby's gun should have really jumped after he fired.
Now look at this film about handgun muzzle flash. It's called: Blinded by the Light.