I think that was because Oliver Stone and Jim D are not far left liberals. I think they might even be considered somewhat conservative.
If you think those people are "conservative" then I'm not sure what political yardstick you are using? I guess you can argue the so-called "horseshoe theory" of politics; that is the far right and the far left sort of merge or come together in some areas. So someone on the hard left resembles someone on the hard right.
Jim Garrison called himself a "libertarian conservative" but his view of America, of who he thought ran the country (the "war state"), sounded exactly like that of the New Left of the 1970s, of the anti-American leftwing, and the "woke" left of today, that views the American project as thoroughly corrupt.
Oliver Stone produced a movie for HBO - "The Untold History of the United States" - that argued that the Cold War was caused solely by the policies of the US, that if we had elected Henry Wallace instead of Harry Truman in 1948 that none of the subsequent conflict would have followed. Yes, poor Uncle Joe Stalin never had a chance <g>. That's a left wing view of US/Soviet relations. It's even further left than what a Chomsky or Zinn said. They at least were critical of both sides.
Both Stone and the DiEugenio are, in my view, on the political left. I have no idea what "conservative" view they hold. Could you give us an example?