Hi dear!^^
Maybe Chaotic could confirm, because I'm not used to modeling in that "fresh" way.
Maybe he use an ordinary cold modeling paste, we can see that this is just one block, so maybe he did a multiple parts mold.
Or this is a bi-components and there is no matter with heat and he don't have to mold it! The best way I think, and he must have done this for sure.
He did it in a month, beetween december and this january.