It was simply a term used to describe someone that wa sa citizen by birth, nothing complex or complicated about it.
That is a common body of thought, but I don't believe it to be an accurate one. I believe the term "natural born citizen" is a "term of art" known to people familiar with international law in 1787, which mostly amounts to the writings of Grotius, Puffendorf and Vattel.
John Jay, who was raised speaking French, could be said to be the Father of the Article II requirement, and his usage of the term implies that it is intended to exclude all foreign influence. Since the founding era, we have created the situation where foreigners can claim "born" citizenship for their children, while possessing no loyalty to the country whatsoever. In addition, we have created these "half and halfs" which would never occur under the circumstances with which the founders were familiar.
Both these "anchor babies" and these "half and halfs" are considered "born citizens" under the current legal misinterpretation of the 14th amendment, but they most certainly do not represent the same sort of allegiance as that which would be expected of a "natural citizen."