It seems that they describe a situation where history is very highly politicized, making it a lot less objective when it comes to teaching.
Not just less objective, less informative. For example, who learned about the Tulsa Black Wall Street in history class? I know I didn't. I didn't learn about that until I was living in Tulsa and read placards on the street talking about it. Who learned that there were Black Wall Streets in more than one city? I didn't, I learned that thru internet research a few years ago. If you did happen to learn of their existence, you probably were taught that it was destroyed in the Tulsa Race Riot of 1920. You probably never learned that they rebuilt after that. Why? Because the actual history of their demise is wrapped up with redlining, and that embarrasses the conservatives in Texas who don't want anybody to know the full extent of what this country did to African Americans, while also embarrassing the progressives in California who uphold FDR as a god.