Agreed with all your disclaimers. The problem was that people did not preplan and train for this situation. You can see that some tried to grab the gun, but cause of the light and missing experience with gun belts (English isn't my first language), they were confused by not being able to draw the gun away from him.

Thus they ought to bring the weapon to the ground and fixate it, so that he can't properly utilize it. However there is a good chance it fails, or that he got a knife on himself, which would just made him stab you.

Him not being arrested likely means that he was able to delete incriminating material on his phone, his room and computer.

In self defense courses the main lesson for encounter with peoples with guns was: get way as good as you can, by running, dodging, hiding – you don't want to charge a person brandishing a short arm.

However if it is necessary to do courses and talk about what to do in such situations seems to be necessary and needs an update.