The purpose of an interview is to see if you fit with their team and if that team will fit with you. You might be given questions for which there is no real answer. They want to see how you will behave under pressure, so they may artificially induce that via bizarre questions. In addition they want to know if you are teachable, and if you are smart and think on the fly. Be super honest because claiming you know something you don't, then falling on your face about it is much worse than being honest. Knowing your limitations and being enthusiastic about learning new things is much better than being fake about knowing some technology.
That being said - why are you interviewing at some place if you don't know the technology they work with? Do some research ahead of time and at least get some kind of working knowledge. Show that you are willing to go the extra mile to get this position.
And, as I said, it's about whether they fit with you. If you end the interview uncomfortable and out of sorts, then that may be a sign you do not want to work with these people on a daily basis.