The answer was extremely rude. Had they said, they got rid of the documents, because they'd valued them differently from Jason, that'd have been rude and disappointing, but maybe understandable to some degree.
At least these things happen. A former landlady of mine had donated a rare and precious motorcycle she inherited from her father to a local museum. When she coincidentally learned about 10 years later that the museum was about to sell it, she bought it back for a lot of money. Donations can sometimes turn out not the way we want.
In my opinion, saying they just kept the boxes was appalling and beyond disrespectful and I think Jason's reaction is understandable. Of course we've only heard one side...