This could explain the bees returning to the hive.
Is the Queen still present and is she marked?
If she is not present then she may of been clipped and is now lost but you still have the bees.
I am only guessing the above, but again if you find Queen cells and you have a very strong now Queenless colony it may be worth doing an artificial swarm, the bees may have a strong swarming instinct and you may lose them with the first hatched Queen.
Only food for thought for your next inspection which should be ASAP.
I agree with Plumberman, shake or brush off the bees and check for Queen cells.