Why would a guy ask if you are single?

I was telling him that I hate most humans and he told that he also hate humans so he asked me if I am single. How is that relevant to our topic of hating humans?

First of all, what would you like to hear?
Then:
it's possible that your conversation about hating humans led him to think that you both share a certain mindset or worldview, which could make you more compatible in his eyes. He may have then asked if you were single as a way of expressing interest in getting to know you better or pursuing a romantic relationship. However, it's also possible that he was simply making conversation and the question was not directly related to your discussion about hating humans.

I think it was relevant to his interest in having some sexy times.