If you still had a doubt the Nikon D850 sensor is produced by Sony well here is your final proof. Astrocn.org dismantled the camera and spotted the sensor code “IMX309AQJ”. This is a Sony sensor as mentioned on Techinsights.com.
The news matters because once more confirms how dependent Nikon is from Sony. And there is no way for them to be ahead of Sony camera in terms of sensor tech unless they move to another manufacturer (is there a better one?) or Sony allows them to use better sensors than what Sony uses on the A7-A9 series (never going to happen I guess).