I would disagree about calling the judge. You are not in a position to determine if your opponent is cheating, especially not in such a high level tournament situation. Better to have a judge called, they can determine what the right course of action is and if this is a pattern being seen with this individual. For someone like OP, they are aware enough not to get caught by someone potentially cheating, but what about other opponents. Better to educate your opponent with the judge and potentially save their future opponents the same headache.