in C, the 'static' modifier, when used on functions, just means the function's scope is limited to the file itself. This concept is not storage-related. However, when 'static' is used on variables, it does be storage-related. In contrast to 'auto' and 'register'.
A good reference for scopes in C is at here.
Another important and easy to get confused pair of concepts is constant-volatile. Reference for constant and volatile qualifers is at here.