Does he really think inviting a friend into his house is inviting the public in? Or does he mean he does things like the exhibition open house thing that some of Cambridge's artists sometimes get involved in? It must be the former since he states every normal house counts - in which case I think he must be wrong, though I'd be interested to see proof.

And I don't think your house becomes someone's "place of work" just because they're fixing your phoneline. Even if it did it would presumably only apply while they were there.