I'm with you, if they are only using the info found here on ancestry then it's not "DNA" confirmed.

They may have used gedmatch or some other site to do "triangulation" along with yDNA tests and then used that info, along with paper proof, to come to that conclusion.

One of my husbands lines had multiple male descendents from different children of the earliest ancestor yDNA tested plus other people got atDNA. They then used that info - along with paper proof - to confirm the lines. They had over 340 people involved including a "line" that had remained in England. The paper proof was the most important thing ... the DNA was useful in confirming the information.

Hopefully someone will come and correct me if I'm wrong, but from what I understand, triangulation is when you have multiple people who are DNA matches, who all match each other, compare the actual area of their DNA where they match. If they all share the same DNA "spot" then they share the same common ancestor.
But they still need a "proven" tree to find that ancestor and the DNA is just extra confirmation.