It's not a non-fiction film. From the IMDb page:
A very realistic interpretation of one of the bloodiest battles of the Vietnam War.
It is a fictionalization of the actual events.
Nearly all - if not all - narrative films carry this disclaimer, even if the people depicted in the film are real people... the reality is, some stuff will be fictionalized for story purposes... some of the characters will be made up either entirely or possibly combined from several actual people. Some names may be changed if the real people (or their families should they be deceased) refuse to give permission to the production company to use their name.
If it were a documentary, that would be different... but this is still a "based on real events" movie... it may as well all be fake because there's no way to know what actually happened and what did not.