I am not surprised in the least.
You're sitting in a crowded, dark movie theatre, relaxing in the air conditioning, maybe you are on a date or out with friends, enjoying a movie. Then a masked psycho comes in throwing tear gas (!!) grenades and firing a shotgun and automatic (or semi? not sure) rifles. You would be unbelievably confused, terrified, and panicking. There would be no chance for the average person, even a skilled 'marksman' to react under extreme stress and take the guy down.
Perhaps a military veteran with significant amounts of combat experience, who happened to be armed, could have done something, but considering the chaos that ensues when an ambush occurs in a combat setting, when you expect to be attacked and are relatively aware of danger, to expect them to react effectively in a domestic setting is asking a lot.