While this is almost correct, you’re getting way ahead of yourself here.
Donald Trump has not yet been charged with any crimes, in regard to these documents. If the DoJ charges him, they will have the burden of proving that the documents contain “information relating to national defense.”
They will not have to prove that Trump didn’t declassify them. Trump may choose to argue that he did at some point secretly declassify them as a defense - but that’s a defense, not a get out of jail free card.
Whether the documents contain “information relating to national defense” is a question of fact, to be determined by a jury.