Why my coworker guy acting this ways?

So there's this guy we work at the same post I notice when I was eating my lunch alone he was just staring at me then smile. And one time there's an office there's no light so l walk to use the computer to scan and in front there's an window I can see someone even If there's no light and I feel like someone was looking at me so I saw him looking at me secretly so l blush and look down after l walked away. So he go back to my post and my supervisor ask some employees to do some training of the machine so this guy was face to me and keep staring at me and smile but me l feel so shy to look someone in their eyes so l look down. And this week I trained the machine I was alone so he looked at me again he smiled next day my coworker ask me to know where she can find something so I pointed my finger and he walked by looking at me.
Why my coworker guy acting this ways?
Post Opinion