You are incorrect that it’s obvious that the gun was fake.
It looks EXACTLY like a Colt 1911 with a rail mount and semi gloss black finish
I was not there so I am in no place to make a fully informed comment, but tactically it might have been smarter to put some distance between the shooter and try to talk him into dropping the gun.
Unfortunately culture and location is relevant. If you saw a Palestinian entering a bus Israel wearing something that looks like a suicide belt, who would have more of a reason to fear then if you saw an American college student at a Halloween party wearing something like that.
Young boys killing with guns is very very common place in some neighborhoods.
I have one like that, is used for training and is NOT a BB gun, it is a pellet gun and is used for training where firearms would be dangerous. It looks and feels just like a firearm. You would have to be inches away before you would be sure. Mine is made by Beeman. The reason for the exact look, feel, and weight is so you will be ready when you have the real thing in hand. It even has a little "kick." I credit my Beeman with helping me keep my Navy "Expert" medal. And yes, I actually had to carry once on one of my active duty assignments in the Contra war.