I think it is likely he hosts it himself. And it is a stretch to include the domain registrar since the service it provides is only one of addressing and not content.
I don't see what distinction you're trying make between "addressing" and "content". In either case he would be dependent on a third party (that he may have to pay for their services) to keep his site online.
He renews his certificate every two years, or his site effectively goes offline. He renews his domain every two years, or his site effectively goes offline.
What's the difference supposed to be?