This is a common misunderstanding.
While your OS has DirectX 11, it lacks the DirectX9 helper dlls. Like many games DeskScapes requires some of these and so you need to install them and the installer is called the DirectX installer. This will not replace any OS files, or downgrade your DirectX on your Windows 8 machine.
The same thing happens when you install a game on Steam and it says installing DirectX redistributables.
Why Microsoft decided to not just include these files in the OS I will never know.
So in short you should allow it to install and the update is perfectly safe and required.