I didn't see the interview, so I probably shouldn't make any comments here. However, what I have read about this latest (Bush bashing) film from other sources makes me suspect that his comment was meant to deflect Katie Couric and prevent himself from being dragged into Bush bashing.
I could be wrong, but it doesn't seem to me that he would leap on that particular bandwagon, although most of Hollywood (and the NY television studios) would like him to do so.
I agree with your take on it. And if he kept talking over the others, it sounds like he didn't want them to get off into Bush-bashing either.