Yep, stupid thing No. 832 by J.K. Rowling.
The Room of Hidden Things version of the Room of Requirment is described as a cathedral-sized space with towering piles of junk forming a labyrinth. Clearly, people had been hiding stuff there for a looooong time before Riddle hid the diadem.
It's not even clear why Ron says, "And he never realized
anyone could get in?" ... when the only way Tom Riddle could have missed that is if he were blind.
So perhaps it's not a matter of Riddle thinking he had the hiding place all to himself, but rather that it was a fine hiding place regardless.
Hmmmm, yeah, doesn't make much sense? Welcome to the Wonderful Wizarding World of J.K. Rowling.
