No, these aren't criminals. Finland doesn't think mad people have somehow committed a crime, it just won't let them leave. They're detained against their will until the doctors decide they've fixed the problem.

Compare the decision not to let your five year old have pudding because she hit her brother and refused to apologise, versus the decision not to let her jump into the tiger pit because she might die. These are both restraints on this kids' freedom, but they come from very different places.