How can you tell if someone is cheating?

So I was just playing some comp and as I’m playing someone in team chat ask if these guys are cheating and I was confused as to why so I decided after that match to watch the replay.

Even after watching it for like a half minute I noticed something strange about the enemy punisher ( note: they got 46 kills 29 final hits and 36% accuracy) I really don’t think its aimbot but I did notice how he would just shoot at nothing randomly during the match, but what I did notice when spectating him how whenever one of my teammates were behind something he was able to see them on the other side of the wall.

I would provide a replay code but I’m not sure if that would be again the rules.

How can you tell if someone in your game is actually cheating?