My guess is those cars are empty or near empty. I say this cuz the flood surge across them must have lifted the car bodies (hollow, empty hopper cars are far more buoyant and lighter in weight than loaded ones) and bogies straight up vertically and then horizontally.... leaving a lot of the wheels (which are solid, dense and heavy.....not hollow steel, making them pretty much the least buoyant part of the car) still in their pair position on the rails or just off the rails.... with exceptions of course. You don't see that happen often.
That implies this was a quick wall surge of water that was rather high at it's head to lift the cars and then lay them gently on their sides on the backside of the surge's crest. Also... the couplers held for the most part with the locos heavy weight acting as an anchor to keep them from washing away.
