It was too eerily fake that this player made instant moves that were in perfect places to take sacrificed pieces or strange and irregular moves to set himself up. .
Premoves are stored client side and the two clients never directly connect. There's no way your opponent could see your premoves since they have no way to get your connection details.
Though if you really think your opponent is using a bot, you can report them: https://support.chess.com/article/209-how-do-i-report-someone
It was too eerily fake that this player made instant moves that were in perfect places to take sacrificed pieces or strange and irregular moves to set himself up. .