The story in The Curious Case of Benjamin Button was narrated by Benjamin himself. When accidentally Daisy was hit by a car, Benjamin explained, in detail, a series of events that caused a little fluctuation in time which resulted in that fatal accident. He also said that if they hadn't happened, there wouldn't have been an accident. My question is, how did Benjamin know all these where he was not present? This looks absurd to me. Maybe some of you have an interpretation!
It’s been a while since I have seen the movie. But, if memory serves me correctly, Benjamin recreated the narration as a flashback. In other words, it was not narrated in real time. In which case, any event can be recreated in retrospect if given enough time and information about the event.
Benjamin would have heard the stories of the incident numerous times during his relationship with Daisy. He also knew her personality and those of the people around her fairly well. He would have been told or guessed details of the accident and the reactions of those involved. He would have taken dramatic and creative license to fill in any gaps. Everything else would have simply been conjecture.
This is the same way accident investigators like the US NTSB put together timelines and causation analysis of accidents. It is part art, part science, part luck. It is not 100° exact and accurate. But, neither is an eye witness account.