It's centering and false empathy. While we can try to blame the American education system all we want, every American adult at the very least knows Black people were enslaved then subjected to draconian laws. Where most white people disagree is the racial progress timeline itself and whether Black people are still treated as second-class citizens. We are.
So if I'm telling a story about a family member who lived during Jim Crow, it shouldn't come as a surprise to another American adult. I see it for the centering tactic it is. White Americans are so uncomfortable with racism that even when it's obvious, they like to be in denial on just how bad it was.
The best thing you can do is match my energy. If I'm matter of fact in my story, then I'm just telling a story.