From the article itself: "It included a racially diverse group of 150 men and women — a rarity in clinical nutrition studies — who were assigned to follow diet

From the article itself: "It included a racially diverse group of 150 men and women — a rarity in clinical nutrition studies — who were assigned to follow diets for one year that limited either the amount of carbs or fat that they could eat, _but not overall calories_." emphasis mine. This particular study is touting the virtues of not tracking calories. It's basically what the entire article is about. Eating low carb without counting calories.