It's complicated :) . While it was indeed made in the 9th century for writing Old Bulgarian (aka Old Church Slavonic), Russia, or rather Russia importing the pr

It's complicated :) . While it was indeed made in the 9th century for writing Old Bulgarian (aka Old Church Slavonic), Russia, or rather Russia importing the printing press, imposed letterform changes to make the letters closer to Latin ones - so you wouldn't need to manufacture too many Cyrillic-specific slugs. There is also the orthographic (spelling) reform that happened under socialist rule. Of course, they ought to have mentioned the origin of the alphabet, considering how often countries' contributions to world history are forgotten or ascribed to their larger, more powerful neighbours, especially given how important Cyrillic was for Bulgaria and the region as a whole.