Not what you’d expect in a rat rod at all, but what would kinda naturally flow from what began as a front-drive rattletrap of a car. The Citroen 2CV is pretty rare here in the US, but they’re common as houseflies in Europe, so it makes sense that people mod them into every conceivable form, as evidenced by this video. There are some who go so far as to convert them to four-wheel-drive.
Since the car is front drive, there is no need to do much of anything with the rear wheels, so the builder took the opportunity to emphasize the rear swingarm. While I’ve never seen a 2CV’s rear swingarm, I can only guess that this is an exaggeration of the original; or maybe that’s just its normal size. From what I’ve seen in photos on the net, both the front & rear suspension consists of swingarms attached to torque tubes, utilizing a funky horizontal spring and shock absorber setup for each corner, similar to a VW’s rear end.