That is debatable. It likely would have ended up in court, had your hypothetical sought the Presidency. He was not an original citizen from the Revolutionary period. He was naturalized by the mechanism then extant, which was a State matter. Articles Of Confederation preceded the Constitution, which imposed the requirement, however he was naturalized as a US citizen, which was precluded.
I'd say it would have depended upon whatever claims there may have been upon him from a foreign jurisdiction and the legitimacy of them, as far as whether he would have been determined eligible or not. By legitimacy, I refer to the disputed claims of England versus, say, France, whose citizenship claims vis-a-vis US citizens would most likely not have been in dispute.
Was he a citizen of the state of Massachusetts at the time of the adoption of the Constitution?
Was he a citizen of the United States at the time of the adoption of the Constitution?
The “grandfather clause” is unambiguous. A citizen of the United States at the time of the adoption is eligible to be President.