There are many glitches in game so it can be hard to distinguish real cheating from the glitch but, let me put it that way, if I'm about to play a competitive game and I get any sort of contact/request from the opposition I'd be wondering about the timing. I'd ignore it but tell my team mates to watch out for anything suspicious in the game. After the game if they want to commiserate or congratulate is different, but before you've started?, there's no reason to message you.