The linked theme looks nothing like the screenshots
On a personal note this is one of the things I disliked about emacs, too: its configs are non-deterministic :) You find a nice config somewhere, or do the same changes,... and your emacs still looks and behaves differently.
Theoretically, another source of deviation might be different distros shipping different builds of Emacs using different flags, resulting in things like different graphics backend (like GTK vs pure X11). I am not sure if this is a legitimate concern in practice, but using something like Nix or Guix might eliminate even that.