Yes, that's some sort of jerry-rigged thing. The machine-side of it once upon a time had the hinge for attaching to LX, E etc. but you can see the hinge has been removed. It also has the center aluminum rim strip like the late AE/F, but then as you point out it does have the Cordomatic logo on the back instead of Electrolux, and it's unpainted. So yes, it's a bit of an odditity.
Yes, I have noticed quite a few Lux model XXX's on eBay. My question is why are they all post-war? I don't think I've ever seen a prewar XXX on eBay. Were that many of them sacrificed to the metal scrap drives of World War II? I've even heard tell that Electroluxes were so popular here in the northeast the dealers would dump the trade-ins in the Atlantic Ocean. Oh, the humanity!