I don’t think he was comparing Robespierre to Franklin. As a rational secular humanist he’s more likely thinking Jefferson, Rousseau, the Marquis de Lafayette and others. Our Bill of Rights, and the French “Rights of Man” and later version in 1793 did not develop on their own, neither jumped full made out of a vacuum. A good treatise on the why and where for can be found here:

ushistory.org

Remember as well that our Bill of Rights wasn’t adopted until 1789, the same year as “The Rights of Man & the Citizen”