It was probably modeled by a "3D scan" of a real dog, then using software to automatically make the base 3D model. After that the artist only has to add the "zombified" last touches.
Maybe the artist didn't noticed those in the final model, it thought it would be too much effort to remove them and then patch the "hole" in the 3D model, or it's for realism (horse balls in RDR2 anyone?).
Maybe the artist didn't noticed those in the final model, it thought it would be too much effort to remove them and then patch the "hole" in the 3D model, or it's for realism (horse balls in RDR2 anyone?).