It doesn't really explain why these cameras are particularly good for use in space except that the crew just like them. All cameras in this bracket are good in low light and have decent long lenses. Why are they any better in high radiation environments than other cameras?
From the article I assume D5 was used simply because it was battle tested and proven, and a an additional Z9 was picked because they fancy the camera and they want to know if it can also be used.
Maybe there's more to it? Otherwise I think personal camera preferences other than radiation performance decides.
Edit: Ah missed the bottom part of it where they mention the Z9 was heavily modified for temp and radiation in cooperation with Nikon.