Official explanation I saw repeatedly:
The cross atop the Black King's head, which is attached by inserting a peg, had either come loose or fallen out. Sevian for some reason chose that moment to pick up the piece and comment.
Things I don't understand: a) Why do it on Niemann's time while he was thinking? b) Speaking during a game is
verboten; c) Why (according to some accounts) did Sevian replace the King on the wrong square?
In other words, I don't understand. Sevian should simply have informed the arbiter of the issue. Background: Sevian (IMO), throughout his junior years, consistently came off as somewhat less than a
simpatico personality. So there could be friction between him and Hans, who projected as abrasive even before the cheating brouhaha and related pressure.
Incidentally, following that round all the Kings' crowns were glued in place. 🤣