Post stall maneuvers are not unheard of in the aerobatic realm of aviation. Do I think the maneuver is possible as shown in the video??? The pilot would have to have been near stall speed already to not break airplane parts. We must remember gents, the pilots of WWII didn't treat their kites the same way pilots treat warbirds today. They treated them more like we treat Honda Civics from the 1990 era

Bent frames and popped rivets were not uncommon, as the skid was a vital part of evasion in this era. We shouldn't discount everything we see on TV as impossible from out perspective.