Feng, I think it's more political than not. I say that because to believe it's not political, you'll also have to believe China would rather partner with Russia than Western aviation companies to gain experience, expertise, and ToTs. That's a hard argument to make, so the most likely scenario is China rather work with both Russia and Western countries, but can't, so Plan B is work with Russia with no Western involvement.
It is not a political thing it is an economical thing.
Europe already has the A-350, A-340 and A-380, China only can be a supplier of parts to such projects.
the USA has already the B-777, the B-787 so the Chinese can only be suppliers too.
Russia has Il-96, but it is an old design, it has 4 engines and a pedigree from 1982, from the Il-86.
It is old, Russia has no B-777 or B-787 and A-380 equivalent.
So for Russia, the Chinese money and Market are the main reason for investment, for China is the share in the project, with Western powers it will have a minority Share, with Russia a 50% share plus the possibility of building 50% of a larger aircraft with much less investment than going alone