Could this have been the reason some of the adf's I bought at petsmart, wal-mart and petco died?
It depends on multiple things, it could have been water quality or the actual quality of the animals themselves. There is no telling with out doing a necropsy on the animals. I am not one to jump to conclusions on this
If you have multiple amphibians in your household you are still safe buying ADFs or any other aquatic frogs. Just use proper Quarantine practices as you would with your fish. Also keep them in separate rooms as well. Do not touch one animal or place your hand in the tank with out properly washing your hands before going to the next. I sanitize all my utensils with a bleach water solution when working with any Quarantine herps.
I hope this helped. It is a devastating disease that is hitting the Amphibian world and many are going or will be extinct due to this fungus. But hopefully we can rescue many species before they even reach the brink of no return.