RT is not only owned by a foreign state but is specifically owned by a state which attempted to deceptively influence Google's home country's elections, partially with the help of RT. RT is undoubtedly Russian propaganda and can't be anything else; anyone at RT who genuinely wants to provide a view that isn't uniformly pro-Russian risks retaliation from the government.
If the scenarios were flipped and Voice of America were peddling propaganda to influence Russia's next election (which they probably actually are doing), Yandex would have a pretty valid reason to lower the rankings of Voice of America stories.