There are some illogical statements in that video, but I DO agree with the premise that merely carrying a gun is not sufficient to stop an attack in any personal defense situation. Defensive handgun TRAINING is the most important controllable element, it's not just about having the means to protect yourself but being proficient enough to implement those means effectively.
It's based mostly on opportunity and surprise. going head to head is always a risky proposition especially when the "bad guy" is a law enforcement combat instructor.
But say you were seated in the upper tears, You ducked when he entered so you could get your gun out and ready to either immediately exchange fire or wait til he is occupied in another direction.
What if you were in the restroom, or a hallway when the attack starts? You cannot tell me that having a gun would not give you an edge.
Whenever possible engage him from behind or from the side.