Most Mormons in Joseph Smith's time likely thought all the peoples of both North and South America were remnants of Israel, including Meso-America, much like you presently believe, say, space aliens could be from the Ten Lost Tribes.
It's just that there was no basis in the text from which to make a distinction.
Joseph Smith however, never spoke of other people than natives of the old US Northwest, from New York through to Missouri, with one allusion to the Rocky Mountains as a place of refuse.
Well, I have read every word Joseph wrote, and every written account of what he spoke, but hey I could have missed something. . .
What about the reference given in the Wikipedia article I linked to above? ”Traits of the Mosaic History Found Among the Aztaeca Nations” article from Times and Seasons, June 15, 1842, Volume 3, Number 16, pp 818-820. This link may or may not take you to that reference: https://contentdm.lib.byu.edu/cdm/ref/collection/NCMP1820-1846/id/9200
Or do you feel that that article is unlikely to have been written by Joseph Smith? (It's just signed "Ed.".)