His paraphrase of the matter is essentially correct. The "wall of separation between church and state" is a phrase that is not in the Constitution anywhere. It was first used by Thomas Jefferson in a letter.
The founders had different opinions on the exact, full and complete meaning of what they collectively thought they were achieving with the 1st amendment's prohibition that congress cannot make any "law respecting an establishment of religion, or prohibiting the free exercise thereof".
Jefferson was a leader in getting state constitutions from separating state governments from directly supporting (through taxes) the dominant church in their state (Congregationalists in Massachussetes, Anglicans in Virginia). He railed at Washington and at presidents who followed for invoking God too freqently in speeches and proclamations and for establishing government holidays in concert with religious holidays.
But Jefferson was also a deist and did not share many other religious sentiments with a majority of the founders. He was often depicted in newspapers, editorials and in congress as an example of Godlessness and evil.
So it is very hard to say, historically, that whatever Jefferson meant by his "wall of separation" statement, it was a commonly accepted and agreed on concept of a majority of those who gave us the first amendment. In fact, the bulk of the historical evidence is that Jefferson was in a minority in that sentiment - whatever it meant. And, the best example of that is, the public and lawmaking practices of most of the other founders and their supporters who later became elected government officials. Their actions did not demonstrate that they shared Jefferson's sentiments with regard to a "wall of separation" and they and their ideas were as foundational as were Jeffersons.
The secular humanist advocates have laid claim to the "wall of separation" as a foundational stance, yet their actions against religion in the public space have, for the most part been against practices that have been considered "Constitutional" since the founding. So who is it that is adhereing to the Constitution and who is abrogating it?
If the secular humanists want some strict definition to the meaning of the first amendment's religion clause, then they can work through the democratic process to get such a definition put in the Constitution with a constitutional amendment. Without that, the courts should respect historically accepted expressions of religion in the public space and quit legislating from the bench.
And this may very well have been his opinion on the matter. But it is most definitely not was the constitution says, nor what anyone, until recently, intended.