Crowd mentality didn't open an exit gate, crowd mentality didn't fail to close the entrance to the central pens, crowd mentality didn't begin spreading lies about those two issues as people were dying in the stands, to cover their arse, instead of doing something to save lives.
It didn't. It did however cause those towards the back, middle, etc. to keep exerting pressure on those in front of them. If you don't have that pressure you don't have a crush. That's why when standing in an orderly queue the person at the front doesn't get crushed however if someone shoves at the back or even bumps once you will get that forward momentum which can have the person at the front flat on their face.
You see the same effect in queues of traffic where one person at the front may drop their speed by 10mph but cars further towards the back come to a stand-still and the distance between vehicles dramatically decreases.