They're referring to psychiatric civil commitment

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.

Incarceration and detention are totally different things. Incarceration is generally for things that have already happened. Detention is for things that might happen in the future. A convicted criminal is incarcerated. A dangerous patient is detained to prevent them hurting themselves or others going forwards.

Sure sure. The motivations are certainly different. However, in both cases, a conscious person is being confined against their will.