Tafney?

Berched talks to us about this "Tafney" when you talk to him about "Nearby Rumors" as if we already know this person. Is there ANY sort of reference to this person OUTSIDE OF THAT?

Not that I know of, but they did the same thing with many other characters too. Nuadha and Aton Cimeni, for example, were first mentioned in C1. It can either be related to future content they are or not yet working on, or may never be seen again in the game. On a side note, he also mentions Tafney when you use the 'Mores' keyword from C1 on him.

It turns out Andras mentions Tafney too.

“	I remember... a human druid, Tafney, I think. That is now another memory to chase.	„
—Andras

Is there a 'Tafney' in the Irish Myth?