Furries arn't "pretend" therians, it's just a different thing, albeit with overlap. Furry's just a general term for anyone with interest in anthropomorphic animals (that is, animals with human characteristics). "Fandom" is just a term for anything related to furry-ness. Most furries also have fursonas, which can be anything from a RP character, themself as an animal, or just a basic alter-ego. It isn't quite the same as a therian's inner animal/wereside/phenotype, although many therians who consider themselves as furries as well will have a fursona based upon their animal nature.