Actually, Bear hand sculpts all his toys. He's not like other makers who use 3d printing, which is why his toys don't have that weird line texture the other makers do!
There are many ways to make a mold.
Here's another that uses deer antlers as an example. This version allows a single sculpture to be used to make many molds.
The simplest molds to make are the "block" kind.
1) Take your sculpture and coat it with mold-release (ex: oil)
2) Suspend in the middle of a block-frame made of fabric
3) Pour your mold material (ex: silicone) in around your item and let it cure
4) Carefully remove your sculpture. The mold is complete!
I don't know the kind of mold Bear uses. Either it's a block mold or has really good seams as to avoid ugly little seam edges.