Without `static`, compiler exports a symbol.

    $ cat value.c 
    int value = 42;

    int get_value() {
        return value;
    }

    $ make value.o
    gcc    -c -o value.o value.c

    $ nm value.o
    0000000000000000 T get_value
                     U _GLOBAL_OFFSET_TABLE_
    0000000000000000 D value

This symbol, not being `const` can be modified by any other compilation unit.

    $ cat main.c
    #include <stdio.h>

    int value;
    int get_value();

    int main() {
        value = 123456789;
        printf("%d\n", get_value());
    }

    $ make main.o
    gcc    -c -o main.o main.c

    $ cc value.o main.o

    $ ./a.out
    123456789

Compiler when generating an object file has to assume the value of exported non-const symbol can change. It's necessary to tell the compiler that the value cannot change, either by not exporting the symbol by using `static` or making the value of it `const`. In example provided in your article `static` makes sense (or even `static const`) as I don't think there is a reason to export this global.