Why would a guy keep staring at a Woman He doesn't know and give her a cocky smile?

On my Commute to work I noticed an attractive guy but I didn't pay him much attention. Later when I looked up I saw him staring and giving me a cocky grin/smile. He looked as if He knew that I found him cute but I‘m usually Not very obvious so I Wonder if He could Really Tell and why he Stared like this? Does it mean He thinks he is out of my league but Im cute enough for a ons?

Why would a guy keep staring at a Woman He doesn't know and give her a cocky smile?
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