From personal experience I think it's a little bit of both, I don't know if maybe it's the way the x-rays go through the camera body itself that accentuate the fog, or if the metal in the camera make them want to examine it further, but in 2010 on my Kodachrome adventure, I went through an airport where they just insisted that they send my camera through the x-ray machine, everyone else that I had been through understood that the film was in the camera and you couldn't take the lens off or open the back and look at it all without exposing the film, but these people didn't and apparently I looked suspicious so they wouldn't hand inspect the camera and send it through, well there was this really heavy banding with all of the images in that roll, it's the only roll out of the, I think 75 rolls, that had any issues, and the only one to go through X-Ray.
This was ASA64 film... This was a "modern" x-ray machine in 2010 at the Key West airport in Florida, small but not exactly backwoods that they would have an older machine.
So I always tell them that the film is 3200 speed film no matter what it actually is and make them hand inspect it, and I always make sure I've used up the roll of film before flying out.
What a waste... They were great shots too...