I think what he was saying is that the calculations (such as on an online TDEE calculator) for maintenance caloric intake are for people without these conditions. Since the TDEE is somewhat reduced with these conditions, a person eating what they think their TDEE should be (by using the online calculator) is actually eating over maintenance, thus gaining weight. What a lot of people don't get is that those calculations are just estimates, and that you have to adjust your calorie intake to fit your individual needs (such as if you have a condition that reduces your TDEE).