It is not the pen, it is the pen tip. Ballpoint pen tips are microscopic tungsten carbide ball held inside ultra-thin steel sockets. So you need cutting tolerances precise to 0.001 millimeters. If the socket is a fraction of a micron too loose, the ink leaks. Too tight, and the pen won't write.
Source from al-Arabiya: https://english.alarabiya.net/variety/2017/01/14/At-last-Chi...
The point (no pun intended) is that China was beginning to crack the processes for making the precision machine tools that make machine tools.
They are not microscopic! I can easily see the balls in the tips of ballpoint pens.
China's ballpoint pen quality as a reflection of manufacturing quality:
" China's inability to produce a complete, high-quality ballpoint pen came to widespread attention in 2015, when Prime Minister Li Keqiang singled out the products at a seminar in Beijing, noting that his writing was "rough" when he used Chinese-made ballpoint pens. For Li, China's failure to manufacture a complete ballpoint pen was indicative of the Chinese economy's weaknesses. "That's the real situation facing us," Li said at the time. "We cannot make ballpoint pens with a smooth writing function." "
https://www.smh.com.au/world/finally-china-manufactures-a-ba...
The ballpoint pen was invented in 1938. It doesn't rely on any arcane manufacturing technology.