No irony: the registrar has to validate the details they have on record. If you have WHOIS privacy set with the registrar, they still have your unmasked details, in which case they contact you on that address, not the one presented in WHOIS.

This is part of the reason why you should use your registrar's WHOIS privacy service rather than some third-party one: by providing the registrar with incorrect details, you're in breach of terms of service ICANN requires registrars enforce.