I hate to answer a question with questions, but...
Would he get close enough to touch you and say "hi" if he didn't like you?
Would he offer you a ride home if he didn't like you?
Would he sit near you if he didn't like you?
Would he tell you "Thanks for being awesome." if he didn't like you?
That pretty much answers your question. He doesn't just "like you". He thinks you're awesome. I think he just wants to know if you like him. That's why he asked "Are you sure?"
About the phone number-
This might not be for you, but I don't have much doubt that it would work for you. Put your number on a small piece of paper and hold it out to him. See if he smiles. See if he takes it.