Regarding heritage, there is some debate as to how common and "pure" heritage strains may be. But when you get into this strain debate, you are forced to define how pure a "strain" must be to call it a separate "strain." Even evolutionary biologists don't necessarily agree on that definition.
So determining wild vs. native strains is going to result in a lot of disagreement. Thus, we revert to something we can all agree on. And that something is that the overall species, brook trout, is indeed native to the area.
For browns and bows, we have a mix of different strains in different streams as well. But the species themselves aren't native, so regardless of the strains, "wild" is the best descriptor.