If you're having the work done at a Camping World, I wouldn't trust anything they say about it. In fact, if it is at CW, suggest you go get it now before they damage any of your equipment.
It would be highly unlikely that it had been a 50 amp and someone changed it to 30. All you need to do to run a 50 amp rig on a 30 amp shore power is buy a $20 dogbone adaptor. Available practically anywhere. The 50 amp cord would hardly fit in a 30 amp head without lots of vinyl tape because it's just physically thicker. Was there lots of vinyl tape?
The only reason someone would want to change that over is because of the weight and bulk of the 50 amp shore cord. But even than, most people would opt for a electric wind up device rather than go to the expense and trouble of trying to convert the RV to 30 amp.
Any chance you took some pictures of the cord or the damage caused by the fire?