Exactly. I have the movie, I will have to check...but I am almost positive the movie say "based on a true story", it was loosely, very loosely inspired by the deaths of two missing scuba divers. That part is true.
They do not know what happened to them after that. They do not even know that they were killed by sharks, they suspect that sharks ate them..but even that could have been after they died. there is no evidence that they were terrorized by sharks or that they argued the way they did or made decisions that they did. Or even that the man died first.
I think it would have been better told as a totally fictional story because they fill so much of the story...90% of it, with fiction.