Drones take 24 days to hatch. So that rules out being laid as an egg last fall/winter. The drones are from this spring. Without the presence of all the rest of normal brood, it would seem that your hive has already swarmed at this point. That would mean you have most likely got a virgin queen in the box (If the bees weren't loud and meaner than normal), however if they were loud and meaner than normal you may be queenless. Did you check the box closely for the presence of a queen cell, swarm cell, supercedure cell?