I believe that you may be referring to that 18th Century author of 'Law of Nations'. You know, the book which our Founding Fathers relied upon at that Constitutional Convention. The same book Washington never returned to the New York library. He used it for guidance for how to conduct himself as President.
No one is saying the Founders were not well-read.
But if Vattel's quirky definition mattered, they'd have enunciated it properly in the Constitution.
But they didn't, and the country went on to solidify the current definition, for better or worse, with the Fourteenth Amendment.