It's referred to as false vivipary if it's a part of a flower stalk. Barry Rice goes into a good amount of detail on his FAQ, but what it boils down to is that since flowers are just modified leaves, some hormonal imbalance could cause the flowers to revert back to leaves. It's perfectly normal in Drosera prolifera and happens rarely in a lot of Dionaea and Drosera. I've had it happen to me before. Apparently you also can cut the plantlet off and root it like a normal leaf cutting.