Someone correct me if I'm wrong, but a garlic plant grows some form of a "seed" head, that will have miniature round bulbs in it if they aren't clipped off that, it's my understanding, when they are planted they'll grow like this in the first year and into a normal garlic bulb year two. I've never experimented enough to know if I'm correct, but if my info is correct I'd guess either one of those got mixed in by mistake, or if your planting in the same spot as the year prior one might've just fallen off.