It is the same thing if he his insulin homeostasis is out of whack. It's a constant struggle in that case. That's why most people who lose weight in the short term gain it right back when they "maintain".
A thin dude at work pretty much only eats junk food and washes it down with regular coca cola, of which he drinks 3-4 cans a day. Every single day. Doesn't exercise much either. And he doesn't gain weight. For me, god forbid I eat a single donut a week, I inflate like a balloon.
He doesn't have to, as he is now at his target weight. He only needs to maintain his current body weight, which isn't the same thing.