To figure out why they might have done it you will need to consider the other body language signals that they are showing.
How do you tell if a man is sexually attracted to you? She may even squeeze your arm.
She always said not to stare at me, even involved teachers, and said I was staring at her and she didn't like it or whatever I was 11 at the time, just starting secondary school.
When an attractive woman walks by, it is almost impossible for them not to get a glance.