If the tank was running in and just pulling then he probably was doing it to initiate combat so that no one could intimate a vote kick. In later dungeon this kind of thing won't be viable as you need active healing, tanking, and dpsing. Personally, I wouldn't heal as an acn with an afk healer but the acn obviously just wanted to get through the run or didn't know how else to handle this.

You didn't do anything wrong. I've been playing this game since beta and have not seen this happen before. Most people in this community are very nice. Unfortunately you're going to run into some bad players who don't care.