I'm going to bet he's wrong but isn't entirely wrong. Their world probably did have magic, but the red fog is something other than the magic their world once had. It's the magic of another world, and it does result in a transformation rather than a regression. There is no reason why magicless food should be corrosive poison to those with magic or food with magic being corrosive poison to those without it. Taking the red fog from the other world is probably detrimental to that world as well if it is magic. End game will probably be restoring the natural magic of the world, and pushing the red fog back to the world it belongs in.