Hmmm, sounds odd. When I get phone calls like that, I usually just say he's unavailable and get a contact number or tell them to ring back later.
I get calls like that looking for our mate, he's lived here a few times.

I get weird phone calls from the blood bank. DH is O-, so they really want his blood (lol). I usually get "Is Jeremy there?" .... "No, he's--" "Never mind, I'll ring him on his mobile" and they hang up in my ear. Joke is on them. DH doesn't get mobile reception at work. It really annoys me.

Honestly, it does sound like a debt collector.
Mum used to get calls like that from the credit card people.