I saw girl looking at me but she jerked her head away. What does this mean?

I looked at her and I saw her looking at me then she jerked her head to the side. I think I also saw her smiling. Though this isn't really too relevant to anything concerning me since I will probably never see this girl again, I am still very curious to know what that means. In addition, if it does mean she likes me, it gives me a huge ego boost. But the problem is that I honestly don't consider myself to be that good looking. I am one of the ugliest guys I know and so no girl I know would ever fall in love with me or think I'm good looking. Though it certainly isn't my best picture, the guy in the profile picture is me.