Man of Honour
Get to a big hill on an eBike and you can tell your legs haven't got it in them? You can rely on the pedal assist. Misjudge how much fuel you needed for your journey and you bonk several miles from home? You can rely on the pedal assist. Those two things happen to you on a traditional bike and your option is to get off your bike and walk or call up for rescue.
That's the point, he turns the motor off on a very heavy bike so he gets way more exercise in a shorter amount of time.
He has the motor off during his session in the woods and then cycles home with a bit of assist.
I can't see how you can't understand how an eBike can get you fitter with more strenuous exercise than a 1kg road bike against a 25kg MTB with the motor off.
Same as my other mate who rides for a proper club, he can do more strenuous exercise in less time on his eBike and then put it on a nice pedal assist which feels like his very expensive road bike to get him home.
You need to ask yourself why some professionals are using them to get faster and fitter.