I didn't really have the Prime
Directive in mind when I mentioned non-interference, but rather whatever regulations Starfleet likely have in place that govern situations when they encounter a spacefaring race are not willing to enter into any sort of relationship.
It strikes me that if a Starfleet ship encounters such a race who politely tells them they're not interested in 'being friends' and to leave their space and not come calling again, then Starfleet would in all likelihood respect this and avoid that region in future.
So if these Sioux aliens fall into this category then Starfleet would likely respect their wishes and not infringe on their territory again, whereas your man on the street
Federation citizen is not bound by the Starfleet MO and can do as they please.