Factual error: Contrary to what the movie states, priests can be elected Pope - they are simply elevated to the rank of Bishop before taking the office.
Suggested correction: Him being only a priest was simply an excuse not to elect him. Those who did not want him to be pope were trying to find any reason to keep it from happening.
Any baptized Catholic male can be elected pope, although it has only happened once. Pope John XIX in the 11th century was a layman, ordained after his election.