More than likely that was a petrol one as diesel is very hard to ignite. Chuck diesel onto a fire and the fire will probably go out.The worrying thing is that a proportion of American Motor homes are petrol...
It does not look like the tank went up as that would have produced a serious explosion. A couple of gallons of petrol could blow the side off a house. Best guess is they left the fridge on and the pilot light caused petrol fumes to ignite, but it is only a guess. and assumes a gas fridge. It could be nothing more than a short circuit and the location was just unfortunate.