That is excatly what you've read. It not so relevant at all, but also something i don't see nobody talking about. Did you know you can change the dry van and flatbed trailer's tandem? For those who don't know, an rigid american semi trailer can have tandems, or not. A tandem is a set of axles, connected to each other within a small structure. This structure is separated from the trailer - They're basically different contraptions. The only thing that makes a tandem part of the trailer is the way they connect themselves. A tandem can be slided through the floor of the trailer, making it possible to set different types of tandem positions. And it is possible to do it in BeamNG. Spawn a trailer, go to its parts section, click on the configs area (Where on a normal car you change tire pressure, suspension, stiffnes, etc) and change the slider for the trailer bogie position. Then have fun with your modified trailer. The more you know, right?
as in the wheel dolly thing? that's mainly so that they can just have all the models/textures for it in the common folder, as it's the same on all the trailers.