The reasons for the general ban on quoting pms or private chats word for word are to prevent angle shooting. Similar to trust tells, you could try to catch scum by demanding a player quote their town pm word for word.
Another reason in mashes is that often closed set ups are impossible to balance around mass claims. mass claims just auto win for town a lot.
And finally if you can post pms then scum will be obliged to make fake PMs to provide when thread demands it. Which sounds tedious, and when we can't even get players to not afk, means lazy town get free clears and lazy scum just die.
Most of the anti pm stuff is to protect scum. Most sites have it as a primary rule similar to trust tells to keep the game playable.
I don't have any idea what happened in this game but I can say
@Mich plays in communities that have a very strict rule on PMs and players not following it is a big deal there.