He didn’t stumble upon them at all. The records department or whatever its official name is said hey we’re missing these documents and think you have them is that the case? And then Biden, but most likely a housekeeper or someone because yes Biden is still an oligarch, found them tucked away and gave them back. Trump was asked by the same people where all these documents were and he said he didn’t have them, hid them, then was busted for having them, claimed he now had the right to have them etc etc.

Edit: oh and the memory and stuff was obviously a side note and partisan dog by Hur. There’s are no charges against Biden because it wasn’t a crime.