The initial file isn’t right, and as written about a billion times do not use photoshop on 16bit files.
As far as how the file looks - are you sure thats even close as to what the map is/was?
Its basically a bunch of steep cliffs and drops to below sea level.
Really it just looks like its not normalized or incorrectly normalized.
Particuarly the center area where it seems like a big valley is suppposed to be seems to have been transformed from a valley to steep cliff dropoffs.
Its possible its right, but its highly unusual.
To view and work 16bit files artistically - which you really should not, ever - use Gimp or Krita or any other program that supposts native 16bit. Ei: NOT photoshop