is he just being friendly or is he interested?

can anyone please analyze for me?

1. he randomly chats me up on facebook and asks about homework problems, but it's not like i'm the smartest in class or we're close friends...BUT weird thing is that he never talks to me about things other than schoolwork

2. he's a shy guy and doesn't say hi to everyone unless with ppl he's comfortable with...sometimes when i see him in the hallway, i caught him staring at me sometimes, and then he'd pause and seems awkward for a second, then just smiles and waves hi, then looks down and walks away without saying anything to me
...e.g. today i saw him walking down the stairs, and he just smiles and says hi, then when he walks past me, he was mumbling sth to me in a very low tone WITHOUT LOOKING AT ME IN THE EYE...i begged his pardon and he just ignored me and walked away

3. somehow instinct tells me that sth is going on...i can sense a special vibe...but i really dont know if i should trust my instinct or if i'm biased because i might be having a crush on him