That doesn't seem to be what happened!
According to the article, the Washington state attorney general, in praising the decision, said "the people detained there are not criminals, nor part of a treatment or rehabilitation program"
They are people in "detention", who are "awaiting civil immigration proceedings".
On the one hand, that makes it seem more egregious, but on the other, it maybe doesn't change the status quo for prison labor as much as one might hope.