Banned twice to be clear means he cheated far more than twice, it more means there were two major periods in his life where he was cheating and chess.com banning him recently implies there was very likely a third period more recently.

That being said I do think it’s unlikely he cheated in Sinquefield. I should stress that OTB cheating and online cheating are indeed psychologically different. One can be a momentary lapse in judgement which can be a slippery slope, the other requires extensive pre-meditation and is more likely to be detected.