He's lucky the BG hesitated... and he didn't. It was clearly a decisive moment. I've been watching quite a few video clips of various incidents lately. What the experienced veterans say is true... Things take unexpected turns (like the BG pushing the clerk hard into the back room, for instance...).
You can see the combination of instinct, adrenaline, and training operating as he simultaneously slaps the BG's gun aside and fires... Thanks for that link. These types of videos are interesting and instructive.