Yes. If there's anything reading diet studies has taught me, it's that people lie, to themselves even, and people are very bad at estimating calories. Things like MyFitnessPal have been a boon to countless people trying to lose weight because they can actually get a handle on what their intake really is. Bonus, they can compare across food choices to see what will fit in their caloric budget but still be filling or satisfying.
I'll issue you a counter-challenge: watch "Secret Eaters".
1. Was the skinny individual monitored the entire time? He could have regurgitated his food.
2. Was the skinny person's poop analyzed for complete digestion of the 4000 calories?The premise of the show is they bring in two people - one superfat and one superskinny. They weight them and each person tells what a typical day's food intake is for them. Then they switch diets for a couple weeks and are weighed again at the end.
Yes, its possible he lied about eating all that chocolate. Yes, he could be throwing up every day. This isn't a controlled experiment, its a TV show. It seems odd someone would do that though.