This is exactly what happened. I am a Horde player on Kil'jaeden and the second I zoned into Isle of Thunder I was killed by literally hundreds of Ruinous players camping the boat you get dropped into.
OP is lying about what Ruinous was doing. They were not running around killing Horde players trying to do dailies. If they were, I would be totally fine with that. What DID happen was a concerted effort on their part to disrupt player access to 5.2 content on day one. SINCE THE SERVERS WENT UP, Ruinous camped that fucking boat for hours on end. Literally. They killed anyone who tried to zone in. They had well over 40 players crowded around that boat spamming AoE spells. What this did was lag the entire zone up horribly, and the server did crash at least once as a result.
OP is lying IMMENSELY about what happened. To call what Ruinous did "PvP on a PvP server" is a gross understatement AT BEST. They were griefing and abusing server capabilities, to say the least. It was literally impossible for us to retaliate because they had caused unbearable lag in Isle of Thunder as a result of spamming spells on the boat.
Proof: http://i.imgur.com/T1TMrFG.jpg