Interesting. And it pretty much accords with the idea that Chi Running does burn fewer calories than inefficient running (although obviously that's not a reason not to run the most efficient way)!
I have to think that when you're outdoors, though, even at foot speed, air resistance is a factor, and the calorie difference would be greater than in the treadmill tests. Heaven knows I notice even a very gentle breeze when I'm running (especially on the beach, running a straight line out and back).