Why did he say hi to me in a quiet voice?

ok so me and this boy in my grade have been making eye contact for a while and and we never talk to each other well yesterday he was ahead of me in the hall and he stopped and right when I got right next to him he said hi in a shy quiet voice and then when I looked back his head was down and walking right behind me...i did not say anything back because I was so in shock but what does this mean thanks