The thing is, there are so many sites being sampled that any one false positive is buried under a mountain of true positives. False positives only matter when

The thing is, there are so many sites being sampled that any one false positive is buried under a mountain of true positives. False positives only matter when you are trying to be definitive about disease diagnosis. That is why clinicians follow up with more sensitive DNA tests after something like 23 and me detects a deleterious variant. For something like ancestry, the number of true positives is so ridiculously large that a few false positives don't matter.