Of course he does not have the knowledgably of the camera, and I suspect he has never taken a picture with a camera using film.
Actually, I think he has SOME knowledge of film cameras; just not with a medium format camera with a removable film cartridge. He's probably shot on a standard 35mm camera where once you put the film in, you can't take it out until you have shot up the whole roll without ruining every picture. So to him, when he sees the first picture of the 6th roll of film used on the moon, and its of a calibration chart, his experience with a standard 35mm film camera tells him that it's impossible that the picture was taken on the moon if the film couldn't have been loaded into the camera until they were on the moon and the first picture was taken on Earth. I think a person would have to be a LITTLE bit educated on at least a basic 35mm camera to realize that it would indeed be impossible with your standard run-of-the-mill camera where you load the film directly into the camera.
In other words, it WOULD be impossible to use a standard 35mm film camera without a removable film cartridge to have 15 rolls of film, and the first picture on each roll is taken on Earth while the rest are taken on the moon. It could not be done with that kind of camera.
It's actually a reasonable error to make. That said, I've had interactions with this person before, and he has no interest in explanations. A reasonable person - upon realizing that in the particular camera system Apollo used, film backs could be changed out mid-roll - would simply say, "Oh, now I get it" and move on abandoning the argument completely. Unfortunately, the uploader of that video is not a reasonable person.
I'd also add that the same concept applies to the 16mm film footage. The first few frames were of the calibration charts, and the film cartridges for those were CERTAINLY removeable.