I wouldn't imagine it is to collect a debt they are a casino not a bookie. Everything (that I know of) that you do at a casino is paid for upfront.
Around here depending on how much you gamble they will call you to offer free hotel nights, buffet dinners, show tickets, etc, etc. Is the person a big gambler?
Why not just ask the person if they live with you. I mean you are close enough to live with them but not ask them why they are calling them?