If you dig up a clump and find them all connected at the base, then you did get a baby bulb that subdivided, but it is also possible that more than a single bulbil got bumped together and it just looks like they are all from one bulbil. If they don't send up scapes, then more than likely there were more than a single bulbil, If they do - well some young bulbs can be very tiny, and it is possible that you got odd bulbs, especially if you planted out early in the fall. It is possible that you have some of both, but most likely there were spots that you planted thicker than you realized. Pretty easy to do with some of the real tiny bulbils.