Oh, I'm agreeing with you. I'd only give it about a 99.9% probability it's bogus. (Nice job, BTW, catching that).
It appears Barton's book is full of fake quotes. It makes you wonder why. In general, the founders were mostly religious men, albeit not always conventionally religious, and it's not hard to make the case that most of them had a less strict view of separation of church and state than we do now. But Madison was an exception. Why did Barton feel it necessary to find a dubious quote to try to pretend somehow Madison didn't believe in the separation of church and state, when he so obviously did? All it did was bring discredit on what would otherwise have been a strong case.
In a reality-based world, that would be the case. But I don't really think that anyone who buys into Barton's premise would have their conviction shaken in the least by knowing that he used bogus information to make his points.
Just on this thread, we've had people state that Terri didn't have a trial, that she didn't have an attorney, that no court other than Greer reviewed the facts of the case, etc. All of those things are demostrably untrue, yet those who have adopted a position ostensibly supported by those falsehoods have absolutely no hesitation about repeating them ad nauseum.
Facts, schmacts is the rule of the day.