If they are refering to U.S. History classes in High School, idk bout the rest of the country, or how other areas currently do it, but when I was in school (graduated in 1997 from High School), US History before 1860 was taught in 8th grade. US History from the Civil War onward was taught junior year. So unless there is something specifically darker below the surface, other than the start date, this strikes me in and of itself as nothing unusual.
That was my thought, too.
“... idk bout ...” I am not sure I would go around holding up the school that taught you to communicate clearly as a model system. High school students should be taught about the causes of our Revolutionary War. They should be taught the philosophy underlying our Declaration of Independence and Constitution (and in the context of what else was going on in the world) on the high school level (or above if they have AP classes). Middle school is an appropriate level to learn the basic facts, dates, personalities; high school is where they should learn the why these events happened, how these documents came about, and the way they effect the way we live our lives to this day.