Not even close. They probably take the estimated fat-free mass (which comes with huge error bars), run it through something like the Katch–McArdle/Cunningham formula, which has IIRC something on the order of a 200 kcal stddev.

Re others having much more junk food and alcohol: you don't see what they're eating when you're not around. I'm one of those "fast metabolism" people, but what that also tends to come with is a very responsive appetite: left to my devices I eat a lot less the day after a big meal.