It is a nice line of propaganda except there is no evidence to it.
Russia is more valuable for China as is. It is providing a market for finished goods and supply raw materials, it builds China an advanced nuclear deterrent including first rate early warning systems, likely to provide advanced submarine submarine technology and much more.
China taking land from Russia is a given and has been seen as inevitable for many years, and that inevitability is getting closer due to Putin’s gross incompetence and incredible misjudgments.