Some people seem to limit themselves by 'rules' others tell them. They see 'dog food' sold at the store, and as far as they know, that's the only food that a dog could possibly eat...and are genuinely surprised that a dog will eat other food. I've seen plenty of people like this...allegedly smart people...who fall into this category. It reminds me of the scene in Blazing Saddles, where the outlaws have trouble finding change to get through a toll booth in the middle of nowhere...unable to figure out how to just go around it.
Great scene from “Blazing Saddles”, and you are right on there.
However, this just makes my BS meter peg out even further. Any human who has ever had even a passing acquaintance with canines knows that except for highly trained and disciplined animals, they almost invariably prefer food that humans eat...if they can get it.