Not to be insensitive or anything but how is that reportable offense?
Edit: I tried to form a group of pugs for TFB SM a few nights ago and some people had to leave after the first fight because their guilds were calling. Was I annoyed? Maybe a little but that is it.
Because they removed him without any justifiable reason, the kick is there to remove abusive players. Kicking someone because he is not a guild-member is an abuse of that feature and that is why it is a reportable offense.
Edit: it is different from what you experienced, you FORMED
the group. The OP in this case used the group finder.