Maybe what made Asian horses somewhat wary of Homo Sapiens when they showed up was their experience with previous migrations of hominids (Homo Erectus, Denisova

Maybe what made Asian horses somewhat wary of Homo Sapiens when they showed up was their experience with previous migrations of hominids (Homo Erectus, Denisovans, Neanderthals). This would assume that these predecessors were less dangerous to horses than were the early humans in America, possibly because they were less widely or more thinly spread, or dispersed more slowly.