Whilst there is a weighting towards Celtic Music, there are lots of people without such a connection. It is a name to avoid "folk" which rightly or wrongly has connotations, most of which are wrong I admit.

Loads of festivals and organisations avoid the word folk. Sidmouth used to be Sidmouth International Festival. Shepley the weekend after next is Shepley Spring Festival.

Wasn't there a festival in Rochester recently? Rochester Folk Festival?

And the Celtic nations of course include Galicia, Wales etc...........

What united Celtic peoples originally was their language religion and culture. I suspect what is left is simply culture.

I doubt such a test could be applied to the Germanic tribes.