I studied the video, and the only thing that I can conclude is that he simply unbolted the pedals from the chain ring. The pedals would therefore not be doing anything at all except support the rider's feet.
The site says "pedaling recharges the battery." This would require re-bolting the pedals back on.
It's hard to see angles that can really make this clear. Maybe there are some freewheels that let the chain ring spin independently of the pedals, which makes no sense to me.
IMHO that would be a safety hazard if they removed it from the rear hub. Without that, the chain will always be moving when the bike is moving. If your pants or anything else gets caught in there it ain't stopping.
Leaving it in the back AND putting it in the front as well is probably viable if a bit redundant.
I have a much simpler kind of bike where this is also the case :)
I was always told that that is so you can use smaller sprockets front and rear for the same ratio, giving you more bottom bracket clearance when you're hopping about the place.
Obviously that's a very specific type of bike for a very specific purpose though.
There was a french company named HXR components which used to produce that, I think they went bankrupt. Nowadays there is the Rocksteady Magic from boutique euro brand Intend: https://www.intend-bc.com/products/rocksteady-magic/