The article is interesting....the wreck is something of a rarity among ship wrecks, in that the stern is embedded in the lake bottom and the now rises at near a 45 degree angle.....I can only recall two or three others where the ship came to rest like that...there's a Russian monitor in a river? that ended up verticle and a British predreadnought in the Med that did the same....
My guess would be, since they were trying to dump railcars, they might have shifted too much weight aft...or perhaps the flooding allowed cars to break loose....