I see where you're coming from, but I also think it's okay to infer people's intent from their statements. In this instance, I feel like the "effects of immigration on the US economy" and "the impact of European migration on Native Americans" are so loosely related that dragging a discussion of one to the other really has to be intentional.

Though, I agree obtuse is probably a poor choice of wording, perhaps I should have said persnickety.