Looks like a real home brew of various bit's of square tube aluminum, strips of polycarbonate, and steel tubes....all bolted together and fastened to the seat post by a couple steering type "dog bones". Pretty heavy duty.

I'm sure it's all detailed someplace on the "endless sphere" site, as he's one of them. Those guys do some fabulous engineering over there, and there isn't any detail about electric bikes and propulsion systems that they haven't covered.