The native populations welcomed Cortez, Pizarro, Columbus, the Vikings (Skraelings), the Pilgrims, the Jamestown colonists, and the Roanoke colonists. Militant distrust by natives on first contact is vastly over-assumed.
Well… Depending on how nitpicky you want to get, shepherds are herdsmen of sheep, with no other difference. The distinction we have now largely comes from the etymology, expanded through usage.
Sheep require less land and food than most other domesticated animals thanks to their diminutive size, and so they’re more likely to find sufficient food within the general confines of a roughly defined “pasture”.
Bovines, which is usually what is inferred from the term “herdsman” (at least in my neck of the woods), require very large amounts of food. I live near some dairies, and the amount of food they have to import daily is staggering. You can’t take a herd of cows up to the highlands and have them graze on the grass there - there’s not enough. They need huge open plains, like the steppes of Mongolia or the savannahs of Africa to survive. The size of the pasture required for the animals is what determines how nomadic you have to be. You’re going to pen your animals in at night regardless of how much feed they require, since you can’t afford to have them get lost, or lose them to unchecked predation. They’re pretty simple to make structures, such as a Maasai enkang, or an Nguni kraal.
Just easier that way. It’s incredibly complicated to compute how much land every person needs for their animals, even if they only have one or two amidst larger groups of herders; there’s no hard limits to what the pasture is in situations like that anyway - just go out further if you want your herd to have fresh grass.