Well, I'm a newb, but since nobody else is answering, here's my guess.
The answer depends. If your friend takes the powder on top of what he's already eating, he will only gain fat if he's not working out. The excess calories have to be allocated somehow, and if the muscles don't have use for 'em, they'll be stored otherwise.
If he takes the powder but removes some fat and carbs from his diet, he's likely to lose some fat and gain some muscle. But it's not gonna be great muscle, and it's not gonna be any overall weight gain.
Basically, this isn't gonna do, significantly, jack shit for your friend. He'll have to use those muscles, or they won't have any need to take in any more calories to be converted to muscle mass.