If you look at the earliest versions of Cyrillic, it's basically identical, in shape and form, to the variant of the Greek alphabet used in the Byzantine Empire at the time, they just added letters for the sounds not found in Greek, like ts, ch, sh, zh. "Invention" is a stretch. I'm not sure why the article spins a political angle so much, it's the same as West Europeans adapting Latin for their needs, except they usually preferred digraphs for non-Latin sounds while Slavs decided to use special characters instead. Cyrillic and Greek alphabets later diverged to look more different from one another, but it was much later.