The article is confusingly written so it's hard to figure out entirely, but obviously her records, or someone already linked to her were in the database.

DNA analysis and the databases are so well populated at this point that they can often "find" missing people via gaps.

Here's an anecdote - In my family an unknown person did a test which connected her to my family, people who already took the test. The system said you must be related to these people. Now my father also took a test but didn't give his personal information, so the system knew both my extended family AND that this person was downstream of my Father specifically but didn't know who he was or how to reach him. She was able to contact other extended family who said my father had the following children, one of them must be your biological parent. The woman was able to easily look at ages and genders at this point and identify her missing biological parent who wasn't in the system at all. Low and behold through the miracle of Social Media, this person got that "Hi, I'm your adult child" phone call.