It doesn't take much. If an elite burns 1500-2000 kcal running a marathon, even ignoring glycogen and exogenous carb, that's only ~195-260g of body fat (~7.7 kcal/g). Even at an extremely lean 4% body fat, Kejelcha would have 2360g of body fat available. (He's probably in the slightly higher 5-10% range.)

(And obviously, the majority of those 1500-2000 kcal are coming from stored glycogen rather than fat.)

If we're only talking about the marginal difference between 90 and 120 g/hr of exogenous carb, then that's 60g over two hours or 240 kcal -- equating to 31g of stored body fat. That's nothing.