It does sound like that is a stock clutch. And any clutch could be gone in 20k miles if someone was hard on it! Aisin is the supplier of the transmission so it would say that on the clutch. Either way it's gone, even if it was 20k miles or original from the factory.
to answer your question, it could be a dealer part or factory. Most likely it would have the same part numbers on it from either source. I know you were trying to see if they were lying by looking at the parts. I'm thinking if was original there wouldn't be alot of heat temp indications on the pressure plate. I know if a clutch is worked hard and abused there would be heat signatures on the pressure plate from over stressing it. If it just looks old, then it's most likely factory.
What are you going to install to replace it?