This case is a good example of why derails are mandatory on side tracks. One would have prevented the car getting loose.
Nevada Northern had a similar incident a couple of years ago when a contractor's loaded flat car got loose (rolled through a pile of dirt substituting for a derail) and severely damaged one of their magnificent wooden passenger cars.
I have to agree with Chris, having something like that happen at either Chama or Antonito seems remote. In both the NN and this case the cars were roller bearing equipped. Having a car break loose on CATS I would think would be highly unlikely.
Just my $.02 of course.
Ned