Calling him mentally ill does not imply it came out of nowhere. It implies that his response to what was done to him was not reasonable, moral, or the reaction

Calling him mentally ill does not imply it came out of nowhere. It implies that his response to what was done to him was not reasonable, moral, or the reaction of what society considers mentally well. Mental instability can mean that something small is more likely to push someone much farther than it should.