"I'm having a hard time imagining the ancient Irish wearing silk. That's my sticking point right there."

Apologies up front, and no personal slight should be inferred, Canuck, as none is implied. A handy example of a prevalent failure of education on languaging.
This line of thought has been responsible for a lot of bad research and poor
scholarship over the years. Diligent pursuit of bias can find "qualified sources" to prove most viewpoints, which can then become "accepted fact". The silk road was bringing trade items to the Mediterranean basin over 2000 years ago, and from there into Europe. People have always been people, and where soldiers and sailors go, there will be children and trade goods left behind. The
average person could not afford such, but it was available, and would have been seen. So, while "the ancient Irish" as a whole didn't wear it, ancient Irish individuals could obtain it, and wear it. Travel was more widespread than we typically realize.