Rick:
I thoroughly understand where you are coming from, but you must understand there is nothing the provider can do to circumvent this issue. Technically, they are being paid for the service by the "neighbor upstairs" and the extension to the person downstairs is technically no different than having another device connected to the main router from within the residence of where this router is housed. We can discuss this setup ad nauseam, but the facts remain that people are going do what they want to do as long as they think they can get away with it.
EDIT: BTW, we do not know if he owns both apartment units. In this case he is simply extending his service downstairs or to the other room downstairs....get it?