I’ve known compulsive liars . They aren’t good at lying during emergencies. When people panic they have a hard time opening up doors without instructions. People don’t make up lies on those situations. Atleast it’s very unlikely. Tweaked or not.

As for mental illness I guess if the person already believes themselves to be a fire fighter because of mental illnesses they might continue that belief on a fire. But again that has to be pretty rare.

Regular guy seeing fire: “this is my chance to lie about being a firefighter”

I doubt that happens often.