I am not authoritative, but I am picky. With steinkerns there is confusion because internal molds are tricky. A mold is a negative impression of the original formed by contact with the original. A cast is a positive impression of the original formed by contact with the mold. Negative = cast, positive = mold. Material or mode of filling does not change this. That is level 1 basics, it can get complex…but, maybe later…
To understand the confusion with steinkerns, consider (for e.g, a statue that an artist makes in clay, molds in plaster, and casts in bronze) that typically a mold is a hollow space and a cast is a solid object. In the case of internal molds, the original is a hollow space and the mold is a solid object. No wonder people get mixed up: a steinkern is a solid object. Negative = mold, positive = cast.