So the Indians, being subjects of a different sovereign nation, were not subject to A14, but Guatemalans, being subjects of a different sovereign nation, are subject to A14. That is something only a lawyer could make sense of.
No, it’s because, putting aside the prejudices of 1800s whites, the wild Indians were present within the territory of their own sovereign power exactly at the same time that they were within the territory of the US. They therefore owed allegiance to their tribe even when they were present in territory over which the US had power. That was not the case with someone who was no longer within the territorial confines of another sovereign of which they were a subject once the game to the US, as the debaters clearly recognized was the case with the Chinese who came here from China and who were therefore still the subjects of the Chinese emperor. That fact was acknowledged as not being sufficient to deny their children birthright citizenship. In point of fact, one of the Senators stated that he would vote against the amendment because it would grant citizenship to the children of Chinese immigrants but not to the Indians.
It’s exactly the same as with a foreign ambassador. Because of the ambassador’s special continuing relationship with his sovereign, he brings his foreign law with him in a way that a mere private individual would not, and does not owe temporary allegiance to the sovereign that governs the country where he is stationed, even though he would if he had simply visited as a mere tourist.
And yes, it does require that you be well-versed in the law, in how to read and apply the law, and how to research the meaning of terms within the law, and that you have a knowledge of things like the canons of construction. Merely having a high-school diploma and passing grades in English class is not enough.