Do guys pretend to not care about a girl when they actually do?

There is a guy in my class in university whom I liked from the first look. He started talking to me about 3 weeks after the start of the course. During the first 2 days he was really nice and actually made me feel that he was interested in me from the way he was talking, the things he said, did, etc. He kept me thinking for about 5 days until we met again (our course is 2 days a week). But now he was different. He seemed like he didn't care, he ignored me several times as he walked by me, and left without saying bye. So, I was wondering, did he just play interested and all nice just to have someone to do the assignments with (he knows I'm really good in that class), or is he actually interested and just playing hard to get?
Do guys pretend to not care about a girl when they actually do?
Post Opinion