This headline is both accurate but slightly misleading.
It is true (as already posted) in the sense that all schools were "divinity schools" in that day....It was commonplace for the educated class to have an education would would rival the clergy and be almost indistinguishable from the clergy. That is extremely significant.
That said, it is not true that they were seminary graduates in the sense that we think of it today....Only John Witherspoon was a clergyman, although two of the others had been clergy in a previous life.
But each of Harvard, Yale and Princeton were basically like seminaries or would look like what we would think of nowadays as a seminary.
Also...John Adams' father was a minister of the Gospel and he desired John to follow in his footsteps, but John chose the law. I'm sure others were the sons of ministers in addition to Adams and Ross.
" while John Adams was the most overtly pious"
I believe Witherspoon would strongly disagree with that...
Also...did y'all know that Ben Franklin proposed once in a letter to the evangelist George Whitefield that they start a colony in Ohio in order to evangelize it and train up the "savages" there to become members of Christian civilization?
Thus...we se yet again what the author of this piece is getting at: even the least religious of the founders were more evangelical than our most religious today.
And Law was more honorable then-lawyers closer to the Divine Law.