How is that different from a password? PIN stands for Personal Identification Number. Words change meaning all the time, of course, but in this case there’s no reason to call it a PIN when there’s already another word for it.
Since the things stored on the remote server have been called “passwords” for decades, it seems helpful to call the local thing a “PIN” to help more easily distinguish it.
IMO it’s not more silly than calling a hand-held computer a “phone.”