He may have his own server. But unless he's huge, he's subletting his access from someone else. Find out who's directly upstream.
Some registrars get interested when a domain under their jurisdiction has no valid contact information. (On paper, all registrars are supposed to care. Whether they really do or not is another matter.) That doesn't mean real name and physical address, just an e-mail address that isn't bounced back as No Such Person.