The W., H.W., Gibson and Stone Conspiracy

A couple weeks ago, Conspiracy Theory was on TV, and I watched most of it. There was a line Mel Gibson said that struck me as interesting, he said something like “Oliver Stone is in cahoots with George Bush.” The weird part is that when the movie was over, I went to sleep, and the very next day was the first time I saw the preview for Stone's new Movie "W." (which was the first I had heard of the movie). Weird.
As to what Mel’s character could have been referring to…
I think he meant the older Bush (the movie was from ’97), who was the head of the CIA in 1976, and in JFK Oliver Stone makes it sound like the CIA was behind JFK’s assassination. (Also, there is some evidence that links Bush to the CIA at the time of the murder and that that was covered-up.)
But how does that put them on the same side?
Well, I guess one result of the public's reaction to Stone’s movie about Kennedy was the JFK Act that Bush signed in ’92 shortly before leaving office. The Act basically created a committee that released all the assassination-related documents to the public (well, they started releasing them and will be done in 2017!). I read somewhere a viewpoint that this Act was kinda just a big show, to look good. Because really all the documents should be available to the public through the Freedom of Information Act of 1966. And documents released by either Act are subject to redaction (blacking out). And some documents are exceptions to the Act, and some have already been destroyed.
So in a way Stone helped Bush and the government look less like conspirators trying to hide something, without them having to really do anything different. The public is pacified by this meaningless Act. Thanks Oliver.
So I think that’s what was meant in Conspiracy Theory. I wonder if that’s a common theory or if they just made it up for the movie to make Mel Gibson sound like a nutcase. I read that the scenes where Mel is talking about his conspiracy theories to passengers in his cab are mostly ad-libbed. He seems like he would have some theories (Jews are responsible for all the wars, right?), so maybe the line is one of his. Note that Mel and Oliver have never worked together. Or, the line could have come from the writer Brian Helgeland, who worked on The Bourne Supremacy (and wrote A Knight’s Tale). The director, Richard Donner, has directed 6 Mel Gibson movies (and The Goonies) and a common theme in his movies is the main character believing something despite others’ doubts.
Anyway, I’m just speculating…but I’m curious: Who wrote that line? What did they mean? And does it have any meaning in relation to the new movie?