How factual it is depends on who you talk to. The Shirley family disagrees with the writer who is the son of the white driver. For his part, Ali apparently apologized to the family because he was told that Shirley didn't have any relatives left.
After the Shirley family made their displeasure with the film known on NPR, Edwin and Maurice heard from Ali. “I got a call from Mahershala Ali, a very, very respectful phone call, from him personally. He called me and my Uncle Maurice in which he apologized profusely if there had been any offense,” Edwin told Shadow and Act. “What he said was, ‘If I have offended you, I am so, so terribly sorry. I did the best I could with the material I had. I was not aware that there were close relatives with whom I could have consulted to add some nuance to the character.’”