I can only assume everyone here is going off their own experience - "I don't know the dress code off the top of my head, so he must not as well".

I think Magnus is under a lot of slow-burn pressure. He's the best, but chess is a grindy game, it only takes one mistake to lose, everyone is watching him, there's nowhere to go but down, and he wants to have fun instead of practice his ass off.

A few tantrums might be a way of getting out of the competitive scene on his own terms.