If someone would have eaten 3 meals for a sum of 2000 cal, with one being a 500 calorie meal, and they decide to switch that out with a 1600 calorie chipotle burrito, then the excess calories they need to burn are only 1100. Which a half marathon would more or less cover.
The situation you described only makes sense if they're eating 2000 calories worth of food during the day then adding an extra chipotle burrito.
Re: your 2nd marathon comment, if someone is eating two 800 calorie meals a day plus an extra 1600 calorie burrito, that comes out to 3200 calories. Minus the 2k resting expenditure, minus the 2k marathon expenditure, they're 800 calories short so they do need to consume more.
Is, I believe, the argument GP is making.
I don't disagree with you, I think the amount of exercise most people are capable of doing on a daily basis the extra calorie needs are insignificant. But I think your examples overstate the point.