I agree. As I said, I'm happy to answer such questions in the interview, though it's not really the appropriate time to question our choice of language. C wouldn't be my first choice either, but that's what we're stuck with. It's not like we're going to rewrite a 20 year old codebase at this point. I'd probably invite the candidate to stick around after all the interviews were over and we could discuss such matters over a beer. But right now, let's just see how you'd code it as asked, okay?
We have several coding problems for various languages, some based on actual product code. I had a candidate tell me flat out that the actual product code was using the wrong algorithm. (Narrator: It wasn't.) He just didn't understand the reason we were doing it the way we were, didn't listen when I tried to explain, and refused to code the solution asked for. He did it the way he thought it should be done. That kind of arrogance is something I don't need in a co-worker.
I had another one who couldn't code C. No worries, we can do this with other languages. What's your best language? He said Python. Cool. Here's a Python problem. Go for it. "Can I access Google? NOBODY codes without Google any more!" Dude, I'm not asking for exotic language features, specialized libraries, or even perfect syntax. You can literally solve this one with an 'if' statement and a 'for' loop. "This isn't a realistic test! It's not fair!" He actually said those words. I thanked him for his time and showed him to the door.
Both these were on-campus interviews with graduating students in CS-related majors, so not exactly "senior positions", but still.