Where was the source of the pop and smoke, as best as they could tell? Presumably whatever it was that popped and smoked is what died.
I would tend to guess that the converter bit the dust. It could be because of a miswired outlet, though that mostly occurs only with 30A RV outlets. If they're plugging into a plain 15A outlet (a standard household outlet), it's very unlikely it was miswired. Likewise, 50A RV outlets are the same as 50A electric range outlets so electricians usually don't get them messed up. 30A RV outlets look a little bit like older 240V 30A dryer outlets, and that's where the confusion and problems come in.
The converter could also have died of other causes besides too high of an input voltage.