I must admit, I had NEVER expected to see that high smite hits, especially not crit, but if you look at it, he's got SUPER low mana and even more +dmg, without any trinkets active his dot does 278 damage per tick, that's higher then shadow specced priests with no +dmg gear...
Well there's the occasional luitenant 2m buff in there since it is Alterac Valley afterall
Basically Priests have a talented spec that'll allow them to DD nuke, like shamans, every 2 seconds. That's unique in the world of warcraft.
Excluding things like a Mage's Scorch since that one has a base cast time of 1.5s, which is terribly inefficient for +dmg gear.