From the thoughts I've gathered from this site, it seems like China has no concern about small anti-American friends (Iran or Venezuela) around the world. However, China extremely cares about Russia. China knew if the day Russia fails or fall, China will lose sleep.
In the past 2-3 years, China companies had went all-in to fix Russia's economic mess because Western companies had left regardless they get sanctioned or not by the West.
Without China's life boat, it is possible Russia will collapse economically and that led to turmoil and unrest like Iran.