That doesn't follow: Ukraine has the international legion (probably about 3,500 people in country last I checked) and a number of Russian groups fighting on behalf of Ukraine.
The only thing Chinese nationals fighting for Russia tells us is that China is not expressly limiting freedom of movement to do so...but there has also been at least 1 American who tried to join Russia to fight Ukraine (and was tortured to death by the Russians on suspicion of being a spy for his trouble).
First, 3,500 is a drop in the bucket. Second, just because China hasn't yet mobilized doesn't mean they won't if they feel a line is crossed like they did in Korea.
With a country like China, everything is on the table
The only thing Chinese nationals fighting for Russia tells us is that China is not expressly limiting freedom of movement to do so...but there has also been at least 1 American who tried to join Russia to fight Ukraine (and was tortured to death by the Russians on suspicion of being a spy for his trouble).