>>509729534 (OP)that is a historically illiterate and retarded take. But nice try, refugee.
The Grand Duchy of Muscovy was created out of the Grand Duchy of Vladimir, which was an integral part of the Rus and even its center of power near the end before the Mongol invasions. Even the people who lived there were the same people who were part of the Rus when it was founded (before Kiev was even a part of it).
It seems like the "Kievan" confuses you, but it's just a word used by historians to distinguish the time frame better, it was not actually called Kievan by anyone ever.
The title "Tsar of all Rus" was likely inspired by the byzantine emperor titles and obviously used "Rus" because they were literally fucking part of the Rus and ruling over much of it. Your "Muscovia" is just retard speech, that's just the duchy that united it, it's like you'd call Germany "Brandenburg"