I'd love to hear this too, I am at 1.7k on Destro. The amount of effort and outplay you gotta do against double melee with endless gap closers and how much you rely on healers to do plays doesn't seem worth playing Warlock in arenas. Gate, Impish, Rift, and melees still close the gap. It's wild.
He's using the spell Unending Resolve or more colloquially known as "walling" which came from the warrior spell "shield wall". Just means he's using a strong defensive.