> I found it odd he turned books upside down to remember he read them.
Unless you have another source, I think you've misread the article.
From the article:
> ...Kim was able to memorize things from the age of 16–20 months. He read books, memorized them, and then placed them upside down on the shelf to show that he had finished reading them, a practice he maintained all his life.
It sounds like he turned them upside down from an early age to signal that he'd read the book (perhaps to his parents?), not to remember that he'd read it. And then, for some reason, he maintained the practice for the rest of his life.
But either way, the article doesn't say he turned books upside down to remember he'd read them.
Unless you have another source, I think you've misread the article.
From the article:
> ...Kim was able to memorize things from the age of 16–20 months. He read books, memorized them, and then placed them upside down on the shelf to show that he had finished reading them, a practice he maintained all his life.
It sounds like he turned them upside down from an early age to signal that he'd read the book (perhaps to his parents?), not to remember that he'd read it. And then, for some reason, he maintained the practice for the rest of his life.
But either way, the article doesn't say he turned books upside down to remember he'd read them.