What does it mean when a guy friend quietly says hi and bye?

[sassycatz]

he's my friend and were pretty close but the thing that seems odd is that he says hi to me in a quietly hesitant voice its usually from far away then he leaves fast. He doesn't do this to anybody else if my friend or his friend is there he will say bye in a normal voice.

[joseyyywhales]

I do this with my friends sister who I really like.

[sassycatz]

why do you do it

[joseyyywhales]

Because I like her?

[selmo93]

Probably shy or feels awkward