Rosa's exchange with Blake ("You may do that.") is exactly the way it happened in real life.
Rosa Parks wasn't the first woman arrested for refusing to give up her seat. Nine months prior, a black teenager named Claudette Colvin refused to give up her seat on a Montgomery bus to a white passenger. Because she was underage and believed to be pregnant by a much older married man (this was later found to be false), it was decided that she was not suitable to be the face of the Montgomery Bus Boycott. Since Rosa Parks' case could take considerable time to make its way through lower-level courts, Colvin's case (along with other plaintiffs) was used as the basis for challenging the constitutional legitimacy of the segregated bus laws. The case (Browder v. Gayle) eventually made it to the U.S. Supreme Court where they affirmed that bus segregation is unconstitutional under the Fourteenth Amendment.
The bus is a detailed replica of the one where the real Rosa Parks was arrested. The original bus still exists and is now exhibited in the Henry Ford Museum in Michigan, USA.
The interaction between Ryan and the waitress was based off an actual event. While playing in the minors, baseball player Vic Power, a black man from Puerto Rico, entered a segregated restaurant in Florida and was told by the waitress that they "didn't serve Negroes." Power responded "Good, I don't eat them!"
With 8.41 million viewers, this is the most watched episode of the 11th season.