Why would this guy rush a relationship?

So a couple of days ago I recieved a friend request on facebook from a guy that I haven't seen or talked too since middle school. After I accepted him we started to chat on facebook and after a while he asks me if I'm seeing anybody and I say no and then we just continue on with the conversation. Well when I have to log off we end up exchanging phone numbers. So today when we started facebook chatting he decided to ask me if I would go out with him. Now I thought he meant on a date so I said yes but it turns out he meant like in a relationship. When I found out he meant this I was shocked because that was so fast. Before today I hadn't talked to him since 2 days before when we exchanged number and I haven't seen or hung out with him since middle school. What I ended up telling him is that we should take things slow before we get into a relationship, talk a little bit more and go out on dates. He didn't have a problem with me saying that and actually agreed with me. He seems like a nice guy but him saying that put up some major red flags. So I would like to know why would a guy rush into a relationship and should I be worried about this guy?