> Are people supposed to suddenly take an interest in some place that they've previously ignored, just because they have some DNA that's commonly found in that location?

Are you American? For most Americans ancestry is an important subject (for many complex reasons), though mostly in a casual way, like sports. Which both explains why the author got upset, but also why they shouldn't have gotten upset.

In my limited experience, I suspect the same is true of many other resettled populations--Chinese diaspora in SE Asia, various Jewish communities, etc. Recording and relaying ancestry is a thing that informs their identity, for better or worse.