Ironically enough, I just spoke with a retired AF pilot about this who used to fly nukes around during this same time frame. He said more or less the same thing but for a different reason. He said they had an arming component that had to be physically inserted into the bombs before they could have nuclear yields and that component was always in the cockpit under the control of the pilot. He told me how much the component weighed but I forget exactly--I think he said about 50 pounds, but made it sound like it was not some token little part. They were prohibited from inserting that component into the bomb anytime they were over the US.
So, unless this was a different type of nuke, I am skeptical this was as close to a full-yield explosion as the story implies.
For whatever it was worth, the Major said that he was certain had there been a nuclear explosion, the USAF would have found someone else to blame because back then it was policy to deny everything related to nuclear programs and policies and accidents involving nukes officially just didn't happen. I snickered because I think blowing the eastern seaboard into the stratosphere might would have robbed them of plausible deniability on that one.