Cool, I appreciate the link. The truth is unclear because there is physical evidence suggesting the contrary. For example, the Nikon D850 is referred to in your link, yet here are teardowns which confirm the sensor wears a Sony part number.[1][2]
And it seems well supported that, historically, many Nikon cameras have Sony model numbers on their sensors.[3][4]
Based on all this, the easiest explanation (and fairly consistent what both of us have shared) might be that Nikon does the design and or specification, and then Sony fabricates. The bar to fabrication is much higher than the bar to design, from what I understand, though I do not work in semiconductors.
[1] http://astrocn.org/thread-3189-1-1.html
[2] https://nikonrumors.com/2018/06/15/new-reports-indicate-that...
[3] https://nikonrumors.com/2015/12/16/list-of-all-nikon-dslr-ca...