There's some confusion about the use of the term 'Celtic'. Irish
music is often classified as 'Celtic' leading some to think that
Irish, Gaelic and Celtic are interchangeable terms. That may be
partly the reason but a general lack of knowledge is also
likely.
The equally Celtic Welsh, Breton and Cornish aren't thought of.
The erroneous 'Welsh Gaelic' is seen at times. A few think there is
a single language called 'Celtic'.