Which, if I understand correctly, is the whole point of the demonstration. You'll lose weight on a calorie restricted diet almost no matter what you eat. So long as people understand that weight loss should not be the sole measure of health, I don't see what the problem is.
The problem is, a calorie restricted diet alone isn't always sustainable. Eg if you're eating crap, but so little that you don't gain weight, it's still going to mess you up (lethargy, irritability, lack of focus).
A twinkie has 135 calories (or 270 for a pair). It isn't a hard thing to fit into your diet if you aren't constantly snacking on things.
On the other hand, if you're riding the razor's edge and trying to do something crazy like get into lower single digit bodyfat while gaining muscle and strength, even a little junk food can make a noticeable difference. I recognize that isn't the typical case though.
Better demonstrations would be: * Compare people eating the same number of calories below requirements, but one on the twinkie diet and one on a healthy diet to see comparative changes in markers * Perform the same experiment as before, but this time with both groups eating the same number of calories above maintenance.