A faculty member who served on many an admissions committee once told me when I was interviewing that, "If you thought it went well, it went well. If you thought it went poorly, it still might have gone well." I think that particularly applies to this case because of what everyone else has been quick to point out, so I wouldn't worry. There's also the intrinsic difficultly of gauging admissions interviews because a rejection/waitlist doesn't equate to the admissions committee disliking you. Interviewers like many more interviewers than they could ever possibly admit, unfortunately. (Yale, in fact, has a second round of review where everyone who was "accepted" from the interview is re-evaluated again in context of the whole cycle. In that vein, both of your interviewers could have approved of your interview and passed you onward in the process but could still result in a waitlist. Just further support that re: a waitlist doesn't mean that your interviews went poorly.)