This is in reference to the source "Traditions and genealogy, lamentably imperfect, of the Mattingly family, 1633-1918", by Father Julius Mattingly.
It does list that Leonard Mattingly was married to Polly Hayden. With that being said, Father Julius Mattingly was of the Ohio branch of the family so his source would've probably been one of the Kentucky family members.
Regardless, it doesn't seem like Polly Hayden as Leonard Mattingly's wife is a new creation. The book was written in 1918.
Traditions and genealogy, lamentably imperfect, of the Mattingly family, 1633-1918
Traditions and genealogy, lamentably imperfect, of the Mattingly family, 1633-1918
Traditions and genealogy, lamentably imperfect, of the Mattingly family, 1633-1918