“based on a true story” wasn’t enough

The makers of The Life of Emile Zola would like you to know that

This production has its basis in history. The historical basis, however, has been fictionized for the purposes of this picture and the names of many characters, many characters themselves, the story, incidents, and institutions, are fictitious. With the exception of known historical characters, whose actual names are herein used, no identification with actual persons, living or dead, is intended or should be inferred.

I wonder if their goal was to get certain historically-minded members of the audience time to walk out before they started complaining.