Possible Surname for Thomas Doran's Father

I've been trying to track down the name of my great-grandfather's father. Looking at my Family Tree DNA matches, I'm seeing a pretty large number of matches with one particular surname as an ancestral surname. This surname is Gallagher. One person that matches some of these Gallagher matches of mine has his only Irish ancestral origins in the Ardara area of Donegal.


Here is a matrix showing matches I have in common with some of my matches.

Every one of my matches in this matrix has Gallagher ancestors except one that has his only Irish ancestors coming from the Ardara area of Donegal. In addition, this match says there are a lot of Gallaghers around Ardara.

Could this mean my great-grandfather's father's father's last name was Gallagher and he was from Ardara? This Gallagher or his parents or grandparents would have come from Ardara to Brooklyn by the 1850s. If so, this makes my direct ancestral tree for my Doran ancestors look like this:

My grandmother - Julia Doran (married to Leo Henry Miller)
My great-grandfather - Thomas Doran (married to Mary Ann Kelly)
My great-great-grandparents - Nancy Doran and ? Gallagher. This would mean that Thomas and Julia's correct surname would have been Gallagher.
My great-great-great-grandparents - Thomas Doran and Catherine O'Hara

I don't know this for certain. It's currently just a theory but I believe it's a good possibility.

Matt