So I was at a subway station waiting for the train and I am leaning against the wall.

A qute girl is walking from the left side of the platform to the right. Now as I am looking at her our eyes meet for a couple of seconds, she lowers her head and looks at the ground while walking. After she walked by me and after 1 meter or so she raises her head and continues to walk normally

Why do girls (or people in general) do that? Is it a I don't like you so don't look at me thing or is it, I like you so I am embarassed and I want to hide?