And throughout that paragraph by Marshall is the assumption that these people's sovereign is their foreign sovereign and that they are merely 'amenable' to the jurisdiction of a country being visited and not SUBJECTS of that country they are visiting.
From the paragraph itself: if such individuals or merchants did not owe temporary and local allegiance and were not amenable to the jurisdiction of the country.
The words "in the United States, and subject to the jurisdiction thereof" in the first sentence of the Fourteenth Amendment of the Constitution must be presumed to have been understood and intended by the Congress which proposed the Amendment, and by the legislatures which adopted it, in the same sense in which the like words had been used by Chief Justice Marshall in the well known case of The Exchange and as the equivalent of the words "within the limits and under the jurisdiction of the United States," and the converse of the words "out of the limits and jurisdiction of the United States" as habitually used in the naturalization acts. This presumption is confirmed by the use of the word "jurisdiction" in the last clause of the same section of the Fourteenth Amendment, which forbids any State to "deny to any person within its jurisdiction the equal protection of the laws." It is impossible to construe the words "subject to the jurisdiction thereof" in the opening sentence, as less comprehensive than the words "within its jurisdiction" in the concluding sentence of the same section; or to hold that persons "within the jurisdiction" of one of the States of the Union are not "subject to the jurisdiction of the United States."