Flirting

What does it mean when a guy gives you a shy smile?

My friend told my crush that I was 21 and he said so, and then she starting about how he was looking for someone who was 21, maybe for alcohol or something but when I gave him a smiled he looked shy, and then he looked annoyed for some reason but towards the end of the day I caught him looking at me with the same smile, and then I asked him who's clothes are these? And he said mine, aren't they nice? And after that, he just giggled at me because I said I was too short.. So yeah I don't know what It means
What does it mean when a guy gives you a shy smile?
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