I’m gonna be that guy: Training Server is to learn. There are the troll pilots and there are the troll ATC. You just have to deal with it. There is no way to really tell whether someone is just new or whether they are purposefully trying to screw with you, so there is no way to report them. Along with that, neither pilots nor controllers can report other pilots in it as well. That’s just the way it is.
Looking at that screenshot, I think I know what happened. When you send that message, it comes up with a response on the controller’s side saying “Roger”. But it doesn’t go away when it is sent like all the other commands. He probably kept pressing it try to get rid of it, thought it was a glitch, and left the session to “fix it”.