Oh and just to nip this little narrative of yours in the bud before you try to continue on with it:
I've had some horrifically under geared tanks in dungeons before, my favourite that springs straight to mind was one with a tank that had ~14k hp vs myself on SCH at 17.5k.. This was also back in the days of cleric stance. But despite that, it was absolutely fine, we had no deaths, the run was clean and my damage was fine. Oh and above all. It was actually really good fun.
So no, I'm of the opinion that given what little we know about events, the healer was every bit as likely to be at fault as the tank. As for why the tank got kicked and not the healer? Where they salty in chat? Did they refuse to release and run back? Who knows? Certainly not me, thus I'm not defending anyone here.