The D1X had a peculiar sensor layout resulting in images with detail smear. Some equalled this to a film-like appearance. However, what result one ended up with for the D1X depended to high degree on the software used for processing the NEFs. Thus, D1X NEFs could be processed to be 10 MPix with the appropriate software, like the famous Bibble program by Eric Hyman, and having much better quality than if processed by Nikon's own software, even when the latter was set to use 10MPix size.
Another factor of importance is the lense(s) used in a comparison. F- and Z-mount lenses are inherently differently designed. I see the actual test was performed with the 75-150 E, which is a medium-contrast, not very high-resolving, optic. The text mentions D1X as having a 5.33MPix sensor which points to the NEFs not being pushed to their limit.