Guys, Looking down and smiling?

what exactly does it mean? this guy has shown several signs of attraction, we have talked and it's not like he's no used to my presence, but he does that gesture that I just find incredibly cute, I don't know if it's shyness or something else. I entered a room and exchange some words with another guy and I looked at him and smiled, he was already looking at me and he smiled back and look down with the cutest smile, like a very subtle giggle... what does that mean?
Guys, Looking down and smiling?
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