Questions about Makkah

Assalamu alaikum dear brothers and sisters. I’ve been having some peaceful chats with my uncle, who’s an Orthodox Christian, about Islam. He’s curious and might even consider reverting, insha’Allah. But he brought up something about Makkah that I couldn’t answer. He heard from some Muslim friends that during prayers there, people sometimes get trampled, and those who pass away are seen as having their souls taken by Allah. He pointed out that at huge concerts, with millions dancing and drinking, there are few if any deaths. I’d love to hear your thoughts on this.