I should have finished the statement:
Again, I say to be of the country, it is necessary to be born of a person who is a citizen for if he be born there of a foreigner, it will be only the place of his birth, and not his country.
To be natural born is to be born of 2 US citizens (plural) owing allegiance only to this country. Otherwise your allegiance is divided.
It is possible for someone to hold a US passport and another country's. That person could be born in the US of two US citizen parents who were born here. For Example, Ireland will issue an Irish passport to someone who can claim that their grandparents came from Ireland. It would be interesting to see if that person could run for President.