It's not exactly a stunt. I've seen several people who eat much as 10000 kcal a day, all of them severely obese. Of course, they're not on a low carb diet, but eating 5000 kcal is a breeze if you put your mind to it. I could do it easily if I wanted to too.

I totally believe he did that and didn't gain weight, but that might not tell us much about people in general.