This is very interesting question! I do think I have some insight, but many of your concerns will probably remain when I am finished!

The benefits are basically economic. The nation state system as it is currently set up, requires enormous sums of expenditures to put on the 'trappings of state' that come with being a recognized country. Things like having embassies in other countries and staffing them can cost millions of dollars - per other country!

In this case, printing currency is not something you can do with an inkjet printer. The realities of currency in a modern age is that it requires extremely expensive infrastructure to integrate ever changing standards of security into the bills. (decentralized currencies anyone?)

China is engaging in a tactic that is very common in other industries, something called economies of scale. They have invested in the best infrastructure around, as well as maintenance and perhaps R&D, and now they want to max their capacity to maximize the investment. They do this by filling orders from other countries.

A country like Poland or Malaysia might be able to get state of the art counterfeit protected bills for a fraction of the cost, forgoing huge infrastructure, training, labor and maintenance costs that come with local production.

I hope this helps a little bit. And I understand if you still have the same concerns as you did when we started! Likely a contract has been signed and if there is evidence of additional printing or other manipulation, a country like Poland would put a claim on China before the ICJ.