I think this is a MacBook Pro peculiarity as it doesn’t (since a late version of Catalina) believe that the actual credentials for an account could be blank. But as long as you can login as guest and do what you want, then that’s ok.
I really don’t think Naim would have added a password during service, not without telling everyone anyway.
The login thing has been there confusing people on a Mac for as long as I’ve owned a Unitiserve. You can safely ignore it, there is nothing that you can’t do through the Guest login.