I'd suggest that the box car on its side with fire oxidation of the aft end was coupled to the other three tank cars in the pic. It was the "buffer" car attached to the rear of the last locomotive. Its position wrt the inside track indicates that it was accurately following the locomotive directly in front of it, but was rolled over by rollovers of tanks cars somewhere to its rear.
Not being argumentative. My whole line of questioning of this wreck is, were the locomotives attached to the rest of the train when they went through town. Just seems odd that five locomotives , unmanned, make it through unscathed and everything else derails. I’ve not read or heard anything officially suggesting sabotage and won’t jump to that conclusion. There must not be any kind of video or it would have surfaced by now