Why would Joseph Smith think Mesoamerican Indians had entire repositories of books?

The Book of Mormon mentions many books being kept, such as in Helaman 3:15

But behold, there are many books and many records of every kind, and they have been kept chiefly by the Nephites.

Bruce E. Dale and Brian Dale explain the significance:

Many books, not just a few, were kept (by the Maya). And in at least some instances, the books were kept together in repositories, essentially in libraries (the “coffers” cited above). The practice is also unusual. What American Indian tribes that Joseph Smith knew of kept even one book, let alone libraries? How did he correctly “guess” this fact about the Maya and the Book of Mormon peoples?
– Bruce E. Dale and Brian Dale – Joseph Smith: The World’s Greatest Guesser (A Bayesian Statistical Analysis of Positive and Negative Correspondences between the Book of Mormon and The Maya)

Why would Joseph describe ancient America as being so advanced?

See:

Bruce E. Dale and Brian Dale – Joseph Smith: The World’s Greatest Guesser (A Bayesian Statistical Analysis of Positive and Negative Correspondences between the Book of Mormon and The Maya)

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