Well, not all US movies are based on true stories. Some are purely the creation of the filmmakers' imagination. But when they are based on real events, they might tweak certain details for dramatic effect or to make the story more engaging for the audience.
Definitely not. 'The Mountain Between Us' is purely a work of fiction. The story and its elements are invented to offer an engaging cinematic experience rather than being rooted in reality.
Sure. The movie is based on a true story. It aims to bring to light the chilling reality of such incidents and might have added fictional elements for dramatic effect.