Surprised that the article doesn't at least mention the fun fact that horses (and camels!) originally evolved in North America, only becoming extinct around 10,000 years ago as a result of the cooling caused by the last ice age.
[next @~1mya (the lower orange (North America) caballine arm from node 3): leading to E. caballus (green: Eurasia) --> domesticated [1] horses]
Regarding the causes of the Late Quaternary extinctions [2] it is pretty hard to pinpoint a single cause e.g. climate change etc. and there are a lot of hypotheses floating around (probably the most curious/spectacular of the bunch: younger dryas impact theory).
But at some point regardless of the causes - approx. 10.000 years ago - there are no traces found of (wild) horses in the Americas, anymore; they only reemerge again with the reintroduction by the European colonists in the 15/16th century.
[0]https://elifesciences.org/articles/29944/figures#content
[1]https://www.nationalgeographic.com/science/article/horse-dom...
[2]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8654998/#!po=32...
But of course one should be open to the possibility, there are a lot of twists, turns, dead ends ... in history (we have very limited datapoints), especially farther afield.
[0]https://m.box.com/shared_item/https%3A%2F%2Fapp.box.com%2Fs%...
I think the horse population where already on the brink of vanishing due to climate change after the last ice age, and the new Americans simply ate the last of them.
It is important to note that those "horses" that became extinct were about the size of large house cats. We have miniature horses today, but the originals were much smaller.