Either he really likes and is shy because you say hi quickly and go. And he thinks you want to keep things casual and were caught in the moment. Or you WERE really only caught up in a moment. If your feelings are real- and they seem to be- be honest and ask him how he feels. It's better than playing games. You don't want him to think you don't care& go looking for someone else to be his girlfriend. If you like him then tell him, and ask him if he feels the same. If he does, he does. If he doesn't then you'll know he's not worth it. And you can find another. Either way, you won't torment yourself any more by playing these guessing games. Good luck.