Since you mention setup instead of any manual install screwery, I’d say root(uid 0) is still very real, you just didn’t setup any login for it. Every time you sudo (substitute-user-do), you(probably uid 1000) are running that command as root instead of you. In fact, just sudo -i and you are now “logged in” as root.
Edit: Missed the context. Should still be useful info but you probably are not accidentally remoting into an account you never setup the login for.