It is never rude to ask what brings a guest to your area, @Dan-and-Julie0. In this case, it seems a particularly good question. "So, [name], you are a host only 10 minutes away from us, I see! What brings you to our place?"
If you just go ahead and cancel his booking yourself, you will be hit with penalties. (Read about them in the Help Centre.) If you are truly uncomfortable with his answer, or non-answer, you can contact Airbnb for help with the cancellation.
Hope this helps.