Except ... he was a Canadian. I mean, who among us can say WHICH of his “birth” citizenships took precedence?
Anyway, he would have had to swear allegiance to the newly formed country on it’s formation to qualify under the grandfather terms. Because in the 1700s the mothers citizenship always mirrored the husbands. In the US.
People have a hard time with that, so I’m providing a cite to bolster your statement on derivative citizenship:
“Just as alien women gained U.S. citizenship by marriage, U.S.-born women often gained foreign nationality (and thereby lost their U.S. citizenship) by marriage to a foreigner. As the law increasingly linked women’s citizenship to that of their husbands, the courts frequently found that U.S. citizen women expatriated themselves by marriage to an alien. For many years there was disagreement over whether a woman lost her U.S. citizenship simply by virtue of the marriage, or whether she had to actually leave the United States and take up residence with her husband abroad. Eventually it was decided that between 1866 and 1907 no woman lost her U.S. citizenship by marriage to an alien unless she left the United States.”
http://www.archives.gov/publications/prologue/1998/summer/women-and-naturalization-1.html