China steels or was given all the US technology.
yikes (steals)
Or, it is stolen Russian technology.
When I lived in China there was a scandal because the PRC obtained three evaluation copies of a new Russian fighter plane. They reverse engineer the Russian plan and built it themselves rather than making a licensed copy or buy from Russia.
Also: since 90s, the massive outsourcing phenomena, particular in high-tech microelectronics and in mid-tech electronics, gave them a critical, unparallel boost.
The outsourcing is always accompanied with technology&process transfer, manufacturing equipment transfer, training, etc., etc., etc. Giving them for free all these years of R&D, fruits of product development effort, means & tools, basic ability to function, etc – the list is endless.