That happens to me a lot. In my dreams I feel like I've known the people for a while even if I dont know them from a previous dream or waking life. Another thing that happens to me is when I know whole backstories to things that happen in dreams. I cant really think of how to describe it too well but hopefully you know what I mean. For example, I'll have a dream about someone who I know in waking life and they get caught for a crime. I'll remember all the previous crimes they commit in my mind while the dream of them getting caught is still happening. Even though havent done anything in waking life. It seems that dreams have a lot more depth than just what appears to be happening in the present, which is really awesome.