Applied to MS in chemical engineering at columbia,
and had an skype interview on this Monday.
It was just a casual interview.
I asked the representative during the interview whether being interviewed means
a positive sign of admission, and his answer was not so much.
Guess the interview is just for international applicants (even with BS degree within the U.S., which is my case).
I would not be too positive about being interviewed, but also don't be too negative about it.
Anyway, good luck for both of us!