It amazes me when folks get hung up on what to call a shape... we are a categorizing, pigeonholing, animal. Personally, I could care less. But, I think of the whole category of dublins as being any pipe that is a bent cone. Then under the dublin category, there are sub categories, yachts, bent dublins, calabashes, horns, zulu, woodstock, etc, etc... When one shape becomes another is clearly in the eyes of the beholder.
The calabash could also be in the bulldog family, because of the cap, making a double cone, but that would have to be in the eye of the beholder also.