I can't say I'm surprised whatsoever; calories in vs. calories out, no matter what they are from. The key difference is mostly the matter of nutritional macro and micro-nutrient content. A Twinkie by no means is competitive with a healthy serving of food concerning vitamins, antioxidants, good fats, carbohydrates, and protein. In other words, a Twinkie (let's say 150 calories) is not going to be as beneficial as a balanced, healthier option (let's say oatmeal, again 150 calories). The multivitamin, vegetables, and protein powder surly helped sustain the body's various needs, but that is not to say that eventually this would not catch up to someone. A multivitamin, even the best, is not going to cover everything good for the body nutritionally.
Then of course is the sustainability, which honestly could swing different ways depending on how else the subject eats/drinks in conjunction with the "junk food."
When the obesity epidemic is brought into play, that last aspect along with self-control become major culprits. Typical junk food is gourged on far past a reasonable serving (and who can honestly eat one cookie?!?), so a moderate splurge becomes a caloric nightmare far exceeding an indivdual's caloric balance to maintain a healthy weight.
As a final point, macro nutrient content becomes very important as it pertains to not just energy levels, blood changes due to high glycemic carbohydrates, and healthy fat benefits, but to body composition in general. Without enough protein, a person could wind up as "skinny fat," which is another undesirable and unhealthy bodily state.
Regardless,the study certainly holds merit because it is further evidence that healthy weight management is constructed partially around the general caloric intake, flying in the face of some of the absurd health claims we are bombarded with every day on television and other media sources.[footnote]See fad diets like "The Cookie Diet" that do not take into account the basal metabolic requirements for the individual for general and healthy sustainability.[/footnote]