Imagine time is relative (just like Einstein theorized) to a person, who could be hundreds of years in the future or a decade in the past. At some intersection, a future person’s future, or death in this case, is the past, in the future; however, another person, in the past, arrives first at the future person’s death. That is this movie.
After all the future has always been known and determined. It was established long ago. It’s only a matter of who will be there.