The first thing that blew me away (ha ha, get it?) was that without thinking, the intended victim's physical reaction was to jerk his head away from the line of fire and to push the gun away with his hand. In Krav we refer to the fact that an effective defense should generally be based on the body's instinctive reactions to a threat. This makes the defense easy to learn, because your body wants to do that stuff anyway. Once you start doing gun defenses in class you'll find that you'll be striving to immediately get yourself off the line of fire & redirect the gun (+ other stuff after that). So seeing this guy do it automatically was pretty cool.
The second thing you'll probably notice is that after he redirects the weapon and it fails to fire, both he & the gunman freeze & stare at each other. I've heard some folks making fun of them for this, but but the truth is, that's the way these things usually play out. That freeze is their brains realizing what they thought was going to happen that day is NOT going to happen and something else - something bad - IS happening. Right now. Their brains (and your brain, should you find yourself in sudden unexpected danger) needs that split second to figure out what's going on and what to do about it.
All this life changing stuff is happening in under 3 seconds.
Next everyone else in the room starts experiencing their own freeze, trying to comprehend what just happened. Then, of course, mob justice. Once one person strikes the gunman, it becomes a free for all. It's hard for me to watch a bunch of people stomping, kicking and hitting a downed individual who is not fighting, in spite of the fact that I just watched him try to murder someone in cold blood (also hard to watch, btw). I know this guy has it coming. I can't say I wouldn't be in there with the mob myself, given the same circumstances. But from the outside looking in it makes my stomach woozy to watch it.