My situation doesn't really fit into your scenario.

When I came out some years ago, I came all the way out. So when someone comes out to me, it's because they feel safe in doing so, almost sort of a "mentor" kind of thing. I'm not "obvious" or flaming, but I refuse to go to any lengths at all to hide it. If someone asks me, "Are you gay?" I just simply say "Yes."

Arliss, the OPs friend may have come out to him just because he felt he could trust him. It may have had nothing at all to do with "gaydar," it may have had nothing to do with wanting to start up a sexual side of the relationship. The first person I came out to was a straight female friend. If I had been that close to a straight male at the time, I would have come out to him first.