If you're talking about finding specific biological ancestors (names) then yes.

But certain general ancestral data can be deduced from variations in your DNA that are observed in some known current/historical population. I.e, I share much in common with people sampled from Scotland -> I must be Scottish.

People are warned not to put much trust into the ethnicity estimates, sometimes even by the services themselves. Telling western Europeans apart is hard.

It's either matching to specific people in the service's reference group who have declared that they are Scottish, or it's trying to guess based on the mix of ancestral populations 2000+ years ago ("western hunter gatherer", "early Neolithic farmer" etc.)