I think the OP should file a complalint with the TSA. The issue in isolation may be trivial, but there's a very important principle involved, or rather two principles: 1) if the question is required by TSA policy, then are we going to accept that the TSA has a right to expand into asking prying personal questions which have no clear relation to maintaining security, and 2) if the question isn't required by TSA security, are we going to accept TSA staff making up their own rules for us to follow on their own initiative?

I would be very interested to know whether this question is required by TSA policy, and if it isn't, whether a TSA staff member who decides to make it part of the standard screening procedure is acting within TSA policy.