Amazon was just the conduit. Someone out there stole these works, repackaged them and offered them for sale over Amazon's site.
This is a very old scenario.
Someone steals something and they sell it to a second individual who then resells it. (Think pawn shop.)
No real title passed so the purchaser was not entitled to keep the item. If the police were involved here and the goods could be recovered, then they would be returned to the rightful owner. The purchaser would get no compensation from the thief.
In this case Amazon was simply being generous by refunding the purchaser's money.
As I said.... don't get hysterical. This sort of thing happens every day everywhere on the planet.