My experience several years ago from biglaw interviewing was that there will always be that one person who tries to rattle you with some sort of impolitic statement and it's up to you to look earnest and sincere and non-offended/upset, acknowledge the position quickly, deflect it and then keep to the path of selling yourself. I would probably have listened quietly then deflected it with, "it's interesting that you say that because one thing I really like about school X is..." I come down on the side of never saying "I'm sorry you feel that way..." because it sounds incredibly condescending to most people so usually I put on my face of "intrigued surprise," widen my eyes and try to deflect as politely as possible with a "That's an interesting data point" or some such boring statement. I agree with never ever slamming other schools or the schools you're interviewing at (which obviously, I'm sure you didn't do). I'd also write this person a pretty nice thank you note and throw in something like "it was great getting a complete picture of the school and having a really open dialogue with you" or some such.
Basically I do approach the whole interview from handshake on as a sales job and it's my job not only to sell myself but why I want to marry the school and have its babies and whatnot.
I didn't face exactly the same thing but I did have an interviewer start my interview with "you know, when I look at this resume the first thing that goes through my mind is that you really don't need another degree..." and I had to kind of quickly rebut it without sounding argumentative.