In this topic we are talking about a sculpted baby from clay. I can see how it's confusing to some as we also refer to the artists doll as which "sculpt" it is from.
Actually the verbage came from the artists original sculpt that they did to create the kit or the doll (in the case of commercially reproduced dolls on the market or in toy stores). The artists had to sculpt their doll in clay (usually) in order for it to be made into a mold for reproduction as a vinyl, silicone, etc kit. This is also considered their "prototype" which you will see if you visit ebay. Sometimes artists will sculpt several prototypes of the one doll they are using to make the kits. I know some artists who will have 3-6 prototypes before they perfect the one they want to have made into a kit or doll to go on the market.