"D3D emulator with OpenGL as the backend" sounds an awful lot like Wine. There've been reports of Wine apps running faster than their Windows equivalent too, although usually some wine bug or another gets in the way of performance.
This wouldn't surprise me. Based on the console output, Counterstrike Source does the same thing. Lots of output about Direct3D that look exactly like messages from wine. I suspect they did this to speed up porting.
