What does a 15 sec stare meen?

So Im big but the perfect friend, I'm not really popular and stay to myself with my like 10 friends, and this guy is really popular but not to terribly mean but we don't really know each other or talk... So I was in math and walking around before clAss and he looks at me strait in the eyes for like 15 seconds and looks away and sits down he just had a calm face and I like raised my eyebrows confused alittle but all in all what does it meen