China itself is interested in weakening Russia, so that these exercises have nothing to say, and especially do not scare anybody. I'm not talking about the fact that the Russian army half a scrap.
Sort of have the same view on this. Join exercises does not mean the ties of the countries are very close. I have seen countries not having good ties with each other doing this to improve relations.
The two superpowers have decided to show the world its power and danger. The whole world already knows that it is better not to mess with them
Don't know about China, but Russia is only an appearance. With the help of China they are trying to scare US, but will support it if China is the question.
Appearance with the largest arsenal of Nukes, which is enough to scare away any other country.