Umm why do girls stare and when caught they look away from me?

Before I go on, these girls were NOT spacing out. They were looking at me from a distance, and when I got close they looked away. Girl number one, I noticed from a distance she was holding eye contact with me, when we got closer I looked at her and she looked away.. Girl number two the same thing, I just happened to glance at her (because she was cute) and I noticed she had been looking at me in the eyes from a distance, I could tell because she looked away when we made eye contact. It's kinda weird. I'm not gay or anything but some girls tell me I'm cute. I'm 6"1- 6"2 light to medium skin and have a slim build. Sooo why do girls do this? I know they're not spacing out because they were looking me in the eye. This was in the hallways at school. I was thinking she was stuck up, but that's the normal look on the girls face, that her normal facial expression. Are they looking at me in scorn because it's kinda awkward.