NVIDIA interview questions

I applied through their website. One week later a recruiter sent me an email about another position, which was wrong. I accept to do the interview which was not interesting for me. So I sent an email back to the recruiter saying that. He finally schedule an interview for the right position. It was a phone interview for about 45 min. The hiring manager asked me about my background and then he asked me a question about OpenGL implementation. He seemed to like my answer but they said I was not a good fit for the position, which I truly disagrees. I don't know if this was the real reason or what.