> Can you point to exact language in agreements that granted them absolute rights to any IP?

Those agreements between private entities are almost certainly not public. However, I found a press release by Siemens AG [1] that says "Part of the contractual terms and conditions involves support and technology transfer in connection with production of the trains." In another press release [2], a Siemens VP is quite chipper about this: "Siemens is even more confident to support the development and modernization of Chinese railways and transfer highly advanced and proven technology of international standard to China"

I don't think you can speak of "wholesale theft" in this case of a voluntary deal.

[1] https://www.siemens.com/press/en/pr_cc/2005/11_nov/tstr20051...

[2] https://www.siemens.com/press/en/pr_cc/2006/04_apr/tstk20060...