I think the only reason for stating that a HD 3850 can run the game is cause it has DirextX10.1. I dont think they have tested to run the game on one. It is ancient. There is even a AGP version. I dont think you can find a motherboard with a AGP slot for one.
This graphics card was the first videocard to ever support DX10.1. The earliest possible card supporting dx10.1 I bet that trainfever do require dx10.1 and thats the reason for stating that this is the minimum requirement.