Apparantly, you can achieve different speeds for the same power if you change the way you pedal on a Computrainer.
Yes, what he's saying is this: If the computrainer needs 400W to turn its roller at 25mph that is the same whatever chainring you use. Physics, gravity and friction still apply. Buy your crank-based power meter may show 395W instead of 400W at 25mph.
This is because changing the to a non-round ring because changing the chain ring introduces calibration and physical differences which are not accounted for properly in the power meter, so it looks like
you are going faster for the same power. Likely this is because the non-round ring has a different stiffness to the round ring and also gives a different acceleration profile for a given pedalling force. So when the power meter samples force at high frequency and integrates it back to power this introduces some measurement differences.
If one could set up a study to somehow show time attained over a course, I'm pretty sure there would be no difference between chainring x and chainring y. I think the results of time trials show that pretty conclusively - qed.
Cycling innovations which promise to give you something for nothing should be regarded in the same way as investments which promise high returns with no risk: Too good to be true.