A good deeper dive into the data would be education level it was taught and county of the respondent. I wouldn’t want to assume without data but my hunch is they learned this in a college/university history course.

I did not learn of this during school in the 90s, nor was I taught about the race riots in 1906. Interesting when Georgia History is required in 8th grade. But my Georgia History course for my Education degree did cover these topics.