I don't think a stranger owes anyone anything in this situation. He might have been vaguely interested but maybe was turned off by something that you said or maybe he found someone else more his type.. You don't know each other, you're each just sifting through possible matches to see if there's anyone you'd like to meet. You thought he might be your type and he for whatever reason doesn't. That must happen frequently with online dating, so you can't let it bother you and also you can't get attached to the idea of a stranger.