I think the term “Unitarian” in this context means general or no specific sect of Christianity.
At least that is how I read it.
Maybe! Well Enlightenment impulses did influence the thinking and religiosity a lot of people of the time, especially the elites. And it was as it still is, common to go through evolutions and phases in one’s spiritual life. Ben Franklin was notably the most secular, but by the end of his life may have exceeded his peers in his faith!