I'm not the least bit surprised. "Therapeutic Martial Arts" has been on the rise for a couple of decades and has a history of documented success. There is a chain of Charter Schools here in Ohio which uses Therapeutic Martial Arts as part of their Gym curriculum (Summit Academy).
One of the Big Shots in our system has, for some years now, run a program for autistic and developmentally delayed kids at a school in Denver.
I've only been there once, as a guest judge for a promotional exam, so I can't judge it's impact personally. But I met a number of kids that day who, by all reports, have really blossomed during the course of their training.
We don't have a specific program, but we currently have two autistic kids in our beginner class, one of whom is really starting to come out of his shell.
I have a family history of depression and a tendency towards mild depression myself. (Fortunately not nearly so bad as what others I know have to go through.)
Martial arts practice is absolutely therapeutic for me. There's no room in my brain for existential angst, worrying about the bills, or general self-doubt while I'm occupied keeping my sparring partner from choking me out.
I don't know that it would be useful for everybody, but martial arts practice is a large part of what keeps me sane and centered.