First of all, it is just a movie. They add such stuff to add some sensation in the movie.

Secondly, the history we are taught in school isn't necessarily true. We are only taught what has been approved to be passed to the coming generations. If we teach our kids that the 65 war started because India invaded lahore, do you think kids in India are told the 65 war started because of India's unprovoked aggression?

Same is the case with Kashmir. They call it Pak occupied Kashmir, we call it azad kashmir. The world calls it disupted territory.

The point is, you shouldn't really trust anyone's writing about history. Just read it for the exam's sake and get done with it. If the boundaries had been determined years before partition, what's wrong with that? They owned the region and had the right to do what they wanted. It is a norm in politics that decisions are made and then executed in a controlled manner to ease the transition and keep the public reaction in check.