Several years ago, my boarding passes used to get flagged for secondary screening frequently, and they'd ask questions along these lines. It is intrusive, but unless the tactic has changed, they're less interested in the answers than in how you act. It's fine to say that the purpose of your trip was "to visit family," or "to go to a conference" and unlike Immigration, they probably won't inquire any further, provided that you don't act nervous or cause a problem.