Since we don't know which movie is being referred to, let's talk generally about the relationship between history and cinema.
The present influences every historical production. There is an influence of the present on historiographical works -- that is, history produced by and for historians, academics -- as there is on movies, fiction books, tv series, etc.
However, historians are aware of this since the first moment of their studies, so they are trained to seek detachment from the present in order to avoid a biased view of the past. But the present is always a strong force and neutrality is impossible. Thus the most plausible way to follow on historical research is to make clear how the present shows in the work, how it guided questions, and turn it into a tool to understand the past.
When we talk about a movie this is different. A historical movie is a different kind of medium -- it's not a paper published after other historians' approval -- and has a different kind of audience than historical research. So it doesn't have the same space to make it explicitly clear how the present influences it; it can not put a footnote when it's portraying historical events and figures so the viewer can check things on his/her own. When we watch a movie we don't have access to sources utilized and on which historiographical line the movie production based its story.
Following from this, basically, you have three possible conclusions:
1) Movies don't improve the viewer's understanding because it is difficult to check if the movie production utilized reliable sources and bibliography. It could portray historical events with absurd analysis, make whopping anachronisms, which doesn't lead to a qualified understanding of history.
2) Movies improve the viewer's understanding of history because, despite analytical errors and anachronisms, it contributes to spread knowledge about the past that can be later improved through qualified studying by the viewer. It can be said movies have an important role in disseminating a historical culture that can be healthy for societies.
3) Movies can improve as much as they can damage serious historical knowledge and the understanding of history. If they are based on qualified historiography they can be important diffusers of a healthy historical culture that helps society to think and rethink its past, present, and future. However, if they spread poor historical knowledge, they can make it hard for good quality history to gain headway.
