Obviously, it appears to be news to Trump.
But it appears he actively hid documents. And if he did that, then he knew they belonged to the government and he was trying to prevent them from having them back.
Why did he try to conceal them?
He had a purpose. I hope the AG can figure out what it was.
Hiding evidence of crimes?
Extortion of subjects?
Value on sale?
All of the above, probably. From Trump's panicky reaction, it was the motherlode. And his usual tactic of delay won't be effective as the documents are already in the hands of the FBI. His problem is that he now has to get the machinery of justice to move. Much harder.