Dominion Seaside cards. Wharf and Outpost in the same hand
Your opponent should have drawn the extra cards on the next turn (the bonus one awarded by Outpost).

From the Seaside rules, about Outpost:


  If you play Outpost as well as a "Now and at the start of your next turn" card, such as Merchant Ship, the turn from Outpost will be that next turn, so you'll get those coins then. 


I think you can replace Merchant Ship with Wharf and get the same result.