Looks like journal bearings, so a hot box would have been a good guess. But since smoke is coming off both trucks I would agree with more likely a handbrake dragging or stuck brake.

Comp shoes really stink when they get hot (like a well used chemical toilet), but these are more likely cast iron brake shoes. I would imagine a hot journal would have an oil stench, but you might get the same from a hot brake if the wheel is oily.