Russians covertly trained by China return to fight in Ukraine, sources say

Why? Russia is the one with more experience training soldiers and more data on how it works out to improve that training. Is it to use some china-specific weapon system?

lol

https://www.telegraph.co.uk/news/worldnews/september-11-attacks/8740536/911-anniversary-Afghan-militants-trained-in-a-barn-in-rural-Sussex.html