Anyone who has foreign citizenship is a foreigner, even if they're also US citizens. By definition, using the legal dictionaries of the period, and specifically using the ones ordered by Madison for use at the Constitutional Convention.
Also, the Minor decision states that those who are born in the US to US-citizens parents form a citizenship class that is distinct from any others that don't satisfy all of the following conditions:
The explicit statement that those membership predicates form a distinct citizenship class does logically exclude anyone who doesn't satisfy the predicates from the class. The fact that the court names this class—and only this class—as "natural born citizens" excludes all those who don't satisfy those same membership predicates from being "natural born citizens."
And it was absolutely legally necessary for the Court to demonstrate that Mrs. Minor was a citizen solely by natural law, and not by statute or by the 14th Amendment, in order for the reasoning they used to justify their principal holding regarding the right to vote to be valid. In order to do that, it was absolutely necessary to correctly ascertain and enumerate the membership predicates of the class (set) of natural born citizens.
Without all the correct membership predicates of any set, it is not only impossible to prove that any missing predicates don't identify set elements missed by the incomplete predicate set, it's also impossible to prove that the missing predicates don't exclude set elements not excluded by the incomplete predicates. That's why the Court had to be certain that it had each and every membership predicate, and no others.
This may be a little off topic, but if the Natural Born Citizen requirement for the US Presidency had also been one of the requirements for access to the secrets of our nuclear weaponry it is highly unlikely that the Chinese communists would have been delivered those secrets. Of course unfortunately political correctness precluded that. And this (minimize the possibilities of divided loyalties) was the reason that the founders who established our Constitution had this as a requirement for the office of the US Presidency. Fortunately the affliction of political correctness did not exist at that time and common sense prevailed.