Where would Joseph Smith have learned about infant baptism in Mesoamerica?

In Moroni 8:5,6 we read Mormon’s concern about infant baptism:

For, if I have learned the truth, there have been disputations among you concerning the baptism of your little children.

And now, my son, I desire that ye should labor diligently, that this gross error should be removed from among you; for, for this intent I have written this epistle.

Here Mormon condemns the practice of infant baptism but what would make Joseph Smith think this was an issue in ancient America? Matthew P. Roper explains that this was indeed practiced in Mesoamerica:

According to Friar Diego do Landa, the Maya of Yucatán practiced a pre-Columbian water purification ritual known as caput sihil, meaning “to be born anew or again.” No one could marry or become a Maya priest without having been thus purified. Children may have been baptized in this manner as early as three years of age. Of the ancient Maya community once located in present-day Mérida, Mexico, Landa recorded, “[I]f anyone died without baptism they believed he would have to suffer more torments in hell than a baptized person.”
– Matthew P. Roper – The Baptism of Little Children in Pre-Columbian Mesoamerica

How did Joseph Smith correctly guess this was a relevant issue?

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