That actually has been disproven, with the discovery of fossils in IIRC 2017 of horses from much later than that, as well as sightings of Natives with horse in the Carolinas in numbers before horses could possibly have gotten to there from escaped or lost Spanish horses, which would have had required the horses to escape or be lost, travel from what is now Mexico City, and repopulate, in 2 years or less.
In other words, the entire narrative that Europeans reintroduced natives to horses has always been bunk “science” based on Western biases.
Edit: a quick google helped me find a good article with links to sources. I’ll do the work for you this time, because I enjoy reading about it anyway.
Yvette Running Horse Collin’s recent dissertation may have rewritten every natural history book on the shelf. A Lakota/Nakota/Cheyenne scholar, Collin worked
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