Derived from baseball dialogue, specifically the New York Yankees, 'did you?!' is a question to reference the certainty (or lack thereof) a player had that his hit was going to be a home run. However the same term can be applied to any situation in which one stumbles upon good fortune, or in which one has a commanding performance or feat of accomplishment.
Derek Jeter hits a home run off the end of his bat that bloops over the wall
Returning to the dugout, Nick Swisher jokingly asks, 'Did you?!'
Derek smiles, shakes his head, and walks by
Robinson Cano *smashes* a fastball for a 400ft homer
Returning to the dugout, Nick Swisher asks/proclaims, "Did you?!!"
Robbie grins and collects his high fives