when a guy smiles at you in the halls... is that a good sign? Options

[rainie8847]

so i just met this guy about 2 weeks ago on a school trip... we stayed at this place for 2 nights and on the last night i went over to my friends' room (guys) and he was there, (sneaked in from another room) so we talked and all and then we ended up sleeping on the same couch (right beside each other) he laid down on the couch and i put my pillow on his leg and slept beside him.

the next day we had lunch and i went out to the balcony with my friends, then he came and stood beside me and we ended up talking a little.

well then after that, at school when he saw me in the halls he would smile and look at me. and i always see him do that first, so i just smiled back. one time i saw him at his locker and went over to talk to him, and i told him how i had a math test coming up and he told me that i should just take it step by step and i'll be fine. we both seemed kinda nervous since i guess we aren't that familiar with each other. anyway.

when i stayed after school in the art room yesterday and today, and he's there because he's in a club or something, n im just there doing my work and all, i feel like he doesn't notice me. like he doesn't even acknowledge my presence. what's going on? i thought he would at least say hi, since he does say hi to me in the halls... sigh. guess hes just not that into me ?