Yeah, it would pretty rare for an American to have an ancestor from Ireland who wasn't white (most, though not all, of Ireland's current non-white population came to Ireland after most of the immigration to the US was over) but it is not all that rare for an American of Irish heritage to also have heritage of color. Or for a person of any race with no Irish heritage to play Irish (or celtic fusion) folk music - folk music subculture in the US does not tend to worry too much about people's genetic heritage if they want to play; and Irish and other cultures have been mixing for a long time in the US.

Also if you want to go for the obscure US racial history points, parts of the US have a history of brown-skinned mixed-race and/or Native American people calling themselves Black Irish in order to get legally classified as white; some communities and families with that tradition have only recently learned their founders were mixed-race rather than Irish as a result of DNA studies.