Other potential reasons behind Magnus's resignation against Hans Niemann

 It is almost evident what Magnus is implying through his actions. Nevertheless we are waiting for Magnus to state what this is really about. But there could be other reasons why he resigned against Hans that way:

1.Hans didn't play the London system:

Everybody knows that London system is the greatest opening ever. After Magnus saw c4 on the board, he realized Hans might be trolling with him by not playing the London system. As a result, Magnus had to resign to save himself from embarrassment.

2.Chess was speaking too loudly:

Hans already said that his chess speaks for itself. Therefore we can't reject the possibility that in this match chess might have started to talk a little too loudly. 

3.Magnus had to go to the toilet:

This is a legit possibility. Magnus could have asked to delay his match. But that would mean whole world would know about this incident. Naturally Magnus decided to resign instead.