Techinically its a mutt. Think of it in the same way they do in the dog world. If you mix to different varities of the same breed , and the offspring has charactoristics of both, the dog is not showable, nor would you use it in a breeding program. Its a mutt.
Keep in mind, mutt just means , the animal does not fit any of the accepted charactoristics of any accepted breed or vairitey of breed by whatever asscoiation you associate with.
These charactoristics or breed requirements will even differ, in some cases, depending on what country you are in.