The fact that they ask this question does show some bias but it may not be as much as you think. I can interview a person and be interested in finding out how much he/she fits like a glove for the tech stack and still put more focus on other qualities. Moreover, I expect a capable dev to not be too judgmental/unconfident and just answer something along the lines:

"No, I'm not familiar with this, but I have done [market themselves, mention relevant experience, ask relevant questions] and I'm confident I can get the job done"