Mistaken ancestry? That's a very American thing to have (not fear). For example, the admixture is such that the African-American population has 20% 'white' ancestry. We're an admixed people. I always thought that was the great part about being American...

Mistaken paternity? That would be pretty lifechanging. But how exactly would a 23andMe style test let you know if you father "wasn't your father?" I suppose he would need to submit DNA as well? (Obviously if your true father is from Asia or Africa but you always thought he was European, you could easily discover this with principal components... but I'm sure that's not what this blog post's author is talking about.)

In my opinion, there is little to be gained, currently, from commercial genetic testing. Groups like 23andMe egregiously oversell their offerings: https://www.23andme.com/store/ "Learn your genetic risk for type 2 diabetes, Parkinson's disease, and other conditions." Please - at present day, your genetic profile tells you no more about your risk for T2D than does your family history.