A lot of "Celtic Witches" will be in deep denial as this knowledge spreads.

The Irish are not Celts.

Probably not the Welsh or Scots either.

The Bretons are questionable too, especially since their language was brought from Britain, not from the Continent.

The DNA of modern Irish predates the first evidence of Celts in central Europe by hundreds of years, at least. The Irish are of a people that migrated from the Black Sea region long before there were any Celts.

This has been shown by analysis of three skeletons found under an Irish tavern. They were in good enough condition to accurately date and recover readable DNA. The DNA matches the modern Irish, but predates the Celts.

Also, researchers are now fairly certain the "Celtic" languages of Ireland, Scotland and Western Europe originated along the Atlantic coast, and predate the language of the Celts themselves - though they belong to the same general branch of Indo-European languages. Evidence from Iberia is thought pretty strong.

It is now believed the Celts never got to Ireland at all, and perhaps not to any of the British Isles. The Vikings did though, and Viking DNA is found in the Irish population.

This new evidence is in agreement with other recent research on these subjects, and so strong it has been accepted even by those who's books on the Irish people now need serious revision.

A good article on the subject, though not the one I learned about this from:
Washington Post.

Probably, the folks who founded, and those that followed the team, just had no idea how to pronounce it. Irish Americans probably didn't know either - they were Irish, not Celtic. This uppity educated stuff came later (it did come, didn't it?).