The experiment is flawed, and the photo shown has nothing whatsoever to do with the vague concept of "the D810's sharpness."
The sharpness in the picture is clearly limited by just about every other possible photographic factor other than the D810, so the D810's "sharpness" (whatever that means) is not even being measured here.
Besides, I happen to have a D810, so how is it that my "D810 sharpness" looks different?
(Note: this is definitely not the sharpest example from my D810. It is also flawed and limited by photographic factors other than the "D810's sharpness.")
The difference is your sharpness is partly due to having a very deep DOF, where as the example from the OP is sharpness within a very narrow DOF. The eyebrow is definitely sharp, it's just that the eyebrow wasn't the thing that should have been the focal point of focus.