As interviewers, we are told by the head ADCOM staff not to ask these type of questions.
At our school, not sure it would be all that relevant as some of our closest competitors do not release decisions until late in the interview season (ie not rolling).
I am sure that this interviewer was trying to do his/her own rogue yield-protection, by trying to judge whether you have been accepted at schools that might be preferable.
I am sorry that you were put on the spot like this. This is wrong. You did the best you could on the spot - I applaud you for answering honestly. To other applicants who do not feel comfortable answering the questions honestly, (or any other uncomfortable question), you can always turn the question around and say "If, by your questions, you are wondering if I am serious about considering going to this school if accepted, I can assure you that I have voted with my feet by coming here for an interview this late in the season; of course I am serious about coming here. Moreover, I have been fortunate enough to have a great interview season that has exceeded my expectations!" That should 1. make the interviewer think that you are really popular and well-liked by other medical schools, AND 2. reassure them that you are serious about their school (which, just by the fact that you are attending an interview there this late in the season, they should know...)