What does this dream mean?

It's memories of your past that's still lingering in your brain. These happen a lot. You obviously knew this person in real life before you even had the dream. Chances are, they're going to be in your dream. I'm not sure about your last question... It could be just coincidence. I've had dreams where I met someone in my dream which I never knew existed. Then later on I meet them... As well as dreams that tell future events. Dreams you have right now are normal and everyone has them even me!