Why is he now cold and distant after flirting with me?

When I first met this guy he was staring with "sexy eyes" and a grin at me for a bit too long. I'm pretty sure he was trying to flirt. However now he is very distant and polite with me while being chatty and chummy with everyone else. Why? Did I give the impression that I'm not interested?

Why is he now cold and distant after flirting with me?
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