Well, some of the information we do know she would have had is quite unique. Like it sounds like the boy told her how many adopted kids the man had, and that they were all boys, which surely can't match up to too many different people. She would have also known that the boy who called was turning 18 within a few days. It was quite a long call so I imagine the details she had would have been enough to narrow in on the correct person if she was able to get in touch with people with access to the right databases.