I don't know if this guy really cheated or not, but from my glance through I don't see even an explanation of the mechanism he would use to cheat OTB.
But this is a cry wolf situation - I would be surprised if there isn't some terms or condition that allows chess.com to ban known cheaters esp from a tourney with such a big prize.
I think it's a fools errand to figure out how he cheated over the board. Small electronic device in a shoe or belt? Someone relaying instructions to him via blinked morse code in the room? At best you're going to suggest something that can't be proven, at worst you're going to suggest something that can, and therefore hurt your accusations.
But this is a cry wolf situation - I would be surprised if there isn't some terms or condition that allows chess.com to ban known cheaters esp from a tourney with such a big prize.