JPK,
I guess you could be right, but I think the guy has been shooting big doubles for long enough to be able to evaluate whether the fault lies with the gun or the shooter.
Regarding the intercepting sears, these don't really prevent a double rifle from doubling.
They can prevent a double rifle from double discharge by catching the second barrels tumbler before it can reach the striker, but in that situation the guns action has still 'doubled' in that the second barrels sear has been accidentally jarred free from the firing of the first barrel.

There is a scene in one of his films where it appears that this may have happened where, after the first shot, the left barrel won't fire and when the gun is broken a fully loaded round is ejected(from the left barrel).