Hey geevikram - sounds like this was a stressful interview!! Usually the interviewers are friendly because they know how tough it is to be n the other side of the table (if it's a student or alum) -- was this interview with an adcom member?
The weight that interviews hold is actually different from school to school, and even from program to program. In general, all the P/T programs are less competitive, and so sometimes those interviews are a little less fundamental to the school's decision-making. They are always important, though - but just because your interviewer had a poker face doesn't mean anything about how you did! Sometimes interviewers are distant like that because they think it shows that they are objective (this happens mostly with student interviewers, in our experience -- sometimes, current students get a bit of a chip on their shoulder in the interview process -- this happens less often with alumni and rarely, if ever, with an adcom person doing the interview). Sometimes interviewers are distant because they're tired - it's exhausting to do a bunch of interviews in a row - or maybe he just broke up with his girlfriend that morning or something! You never know what the reason is, and it's highly unlikely that his attitude is any reflection on YOU.
The stress you're feeling is understandable but this is in the category of "something you can't control" and so just don't worry about it. We're sure you did the best you could, so congrats on that! (We're also sure that we're not helping much with our attempts to be a cheerleader, but we're trying!!)
The best way to bounce back from something stressful, we think, is to tackle another application -- are you trying for Kellogg P/T too? If so maybe you can make some progress on your essays! Or just go have some fun today, you deserve it.
EssaySnark