A restaurateur who only makes money because they own real estate seems like a landlord with a side hobby.
He may refer to himself as a "restaurateur" or a "restaurateur who is his own landlord" for social status or tax reasons but I am suggesting that this framing is misleading: if his income is primarily as a result of the real estate he owns then his actual occupation is "landlord".
Non-remunerative avocations like, I don't know, building wooden sailboats, painting, community theater, photography, gardening, raising cattle, or managing a restaurant may be intense and rewarding, but if the expectation is that they will have no marginal impact on income one way or the other then they are more like hobbies.