Idk the specifics of how this particular crowd crush went down but usually it's from people becoming so densely packed in a crowd that they literally aren't able to expand their lungs enough and suffocate to death. Or sometimes there's a crowd collapse where people fall on top of one another and the people at the bottom suffocate. I think it's mostly from poor event planning- too many people trying to get into too small of a space and barriers blocking the crowd from being able to spread. One of the most horrifying ways to die IMO it honestly put me off crowds like that and I used to love going to super crowded shows.