It could be that he's just naturally more comfortable with a wide stance. I've always been a narrow stance kind of person and always had straps set as close as I could get them.
I think at the mechanical level the wide stance smooths out the pitch inputs as you ride. A narrow stance means a small input has a large effect so the foil is pitching up and down as you ride. Those up pitch moments can cause a bit of porpoising and really slow you down.
As has been said, with wide stance you can move your rear foot further back and that lets you put more power into the foil and results in greater speed.
After a downwind run I often lock in the wing and widen my stance the speed upwind feels much higher ... until I get out of whack and crash.

I'm not sure about the hips forward stance. You see that in all the pictures of kite racers. The only time I have used that is kite foiling and having my straps set out of balance for the foil so I have to unnaturally pressure the front to keep the foil down. It's really uncomfortable.