That "DirectX 9" is a generic one.
The game can force 2 renderers:
DirectX and
OpenGL
DX11, DX10 & DX9 are backward compatible and they depend on your OS and graphics card.
By default:
Windows XP : DX9
Windows Vista : DX10
Windows 7 : DX11
The older graphic cards are limited to DirectX 9.
For example, if you run GeForce 8600GT (a DX9 card) on Windows 7 (DX11),
your graphics card is running in DX9 mode.
