invalid name "g"

There is a guy called "g" that came on my server and told everyone that he's hacking minecraft because he's got such a cool name and i saw that the minimum for creating a name is 3 chars but he has 1 char can i ask how? and how do i get a name like this it is also not correct that he has a 1 char but i cannot make 1 char or 2 please mojang FIX