There was never any evidence of this. The best explanation I heard is that Magnus’ company was merging with chess.com right before a tournament, and with that the information of cheating bans were made available to him. He found out that Hans had been banned for cheating a couple years prior on chess.com. Speculation is that this put Magnus on tilt during his match with Hans, and losing just confirmed Magnus’ suspicion that Hans is a cheater IRL as well as online.