No problem, congratulations on Dawnguard. It was from those who have donated to Skyrim Forums, which, funnily enough, was from The_Deadliest_Troll. Since the DLC costs around $20USD, of which Troll donated $10 to become premium, he therefore has contributed to 50% of your Dawnguard and thus your gift is technically from Troll. So yeah, good on you, Troll :)