It could be about various things. Maybe it's about a real - life experience in a war - torn area, or a situation where people are in a very unfriendly or dangerous place. Without more context, it's hard to say exactly.
It's hard to say for sure. Sometimes movies claim to be based on true stories but take a lot of creative liberties. 'Hostile' might fall into that category.
Yes, it can. A story's tone can definitely be hostile if the plot, characters' interactions, or the overall atmosphere convey aggression or unfriendliness.