Goblin, the Germanwings pilot had considerable mental health issues so it is entirely relevant to the discussion. I agree, he murdered a plane full of people but mental health issues don't fit into neat boxes and manifest in many different ways.
For instance my wife suffers psychotic episodes every few years and she exhibits exactly the same sort of thinking as the woman in this tragic story, except her behaviour is very fortunately only bizarre but not dangerous. They believe all sorts of weird things, and to them it is utterly real.
Why my friend who killed her two-year-old daughter isn't an isolated case