How did they cheat? Obvious cheater in Halo betray-banned me without me firing a single shot?

So this player (BionicBark94176) was obviously cheating in MCC. Literally flying around the map, clearly using an aimbot and wallhacks. I betrayed them once because I got stuck in like five games with them and they were so obviously cheating. After that, they would approach me then it would say I betrayed them when I literally had not fired a shot.

How does that work?