It's in the article. Aflack and Damon are not just the actors. They co-own and run the studio producing the film. They hired a person from the police department in question to consult on the film.

And, to be clear, this isn't the police department being mad because this paints them in a bad light. The film starts with events based off a real case, but moves into a fictionalized narrative where two cops murder a supervisor while working for the cartels. The cops the characters are based on are suing because people know that the characters are based on them and don't realize the rest of the narrative is fictionalized.

Your answer is in the article.

Tbf I would take any opportunity to sue Adobe, logic be damned.