I love any programs in the prisons that is such a win/win like that (they do this with shelter dogs for adoption and some train as service animals, too) I'm unclear why the horses are being trained for adoption at all - because in the wild they are just struggling too hard to survive?
Yes, it was an attempt to get some of the horses off the range. They were overpopulating and indeed starving, and also making the other animals, particularly deer, starve too.