Either he:

1. Recorded a video of him driving a car and frantically pressing the horn

2. Made a screen capture of Doom that matches the gun fire, turns, and weapon changes perfectly to his car video

3. Did some video editing to superimpose the video including several cases where his thumb goes over the screen while shifting

Or....

1. He put software on the car console (which is pretty much a full computer)

2. He actually mapped the controls to data being read from the onboard computer

I mean, I couldn't do this... one I don't know how to write software for a Porsche console and two I can't afford a Porsche :-P but faking it seems like way more work and worse ROI than actually doing it.

Edit: alternatively in some cars the console actually takes RGB or HDMI input and you don't even need to run directly on the console assuming ODB-II has enough info to read the input signals. I can totally see myself doing this if I had the time. Seems fun (albeit a bit dangerous for my taste)

Edit 2: It could still be a fake but it's not unreasonable to think it isn't.