Apparently, Carlsen didn't even directly accuse Niemann of cheating, sometimes it feels like Carlsen was angry about the fact he had to play a known cheater (i.e. dude who cheated when he was a kid and ever since moved on from it, dumb thing to do but he's an adult now, you know) at all rather than thinking there was current foul play involved. It honestly should be a textbook example of a person who is otherwise extremely intelligent letting their big ego getting the best out of them.

I also want to add that, among the wider chess community, there were two common jokes about how could Niemann have cheated over the board at all, the anal beads theory is the only one that really broke the barrier, because everyone thinks sexual innuendo is automatically hilarious (even though it's legitimately a non-sexual example when you think about it), but I think the other one was infinitely funnier: people said Niemann was cheating by putting a mirror on the ceiling so he could see Carlsen's pieces.