I assume you were flustered by that point due to a previous interview, and feeling a little frustrated or defeated. I've been there, when I think it's not going well but they still want to talk.

Nevertheless, it appears to me that those were setup questions for his real problem to figure out how to explain it. If you had approached it with a more open mind, you may have gotten the job. You would have at least heard the question.

I know that most people here hate the Google-style algorithm problem, but I think the question he was going to ask would be about computing the nth prime or counting the primes less than k.

I will also point out that many people who know nothing about number theory know that there are infinite prime numbers. It's not necessarily redundant.