They most likely went through logs and searched for "who queued into a match and did 0 damage/actions" and handed out warnings accordingly. It was definitely enough to scare people for sure.
Edit: I will say with the frequency we are seeing pvp being changed/addressed this time around, it is for sure a huge step in the right direction as opposed to before. I just hope they actually do some serious kind of cheat detection in regards to arenas. Nothing kills my motivation more than almost killing someone who then flys away at the speed of light while heavied.