Oh bull!
Seems I recall there being MILLIONS of bison when the Europeans arrived!
Good grief! Horses and gunpowder, Elsie!
The horse arrived in the New World with the Spanish settlements in the southwest. We tend now to picture the Indian on horseback (at least the Western tribles like the Sioux and Cheyenne, less so the Eastern groups like the Algonquins and Iroquois). However, even in the western cases, their "traditional" lifestyle had changed radically only a few generations before.
Gunpowder was a European import as well. Prior to these innovations, the native Americans were very limited in their ability to kill buffalo, especially on the open plains where the herds thrived in the greatest numbers. Think about it. You're on foot. You have a bow and arrow. There's a buffalo herd over there. It's wide open country. You see them. They see you.
You and your buds do tricks like trying to slowly, slowly crawl up to them while cloaking yourselves in the hides of dead buffalo. Once in a while it might work. You're not going to have a big impact on a prairie that's loaded to capacity with buffalo.
Not very many of the bison were in central Mexico.
Not on the Pacific coast which was the context of my post that you pulled a segment out of. Yet still perhaps I should have been more detailed--or stated a caveat against categorical reading.
Large areas of the midwest where the buffalo roamed were not well populated with humans due to a lack of iodine in the soil although some prehistoric tribes of mound builders were believed to have trade routes for seasalt. Some tribes consumed the ashes of their dead as a condiment, presumably for minerals.