I think that the underlying Daniel Cassidy article (which can be viewed by clicking on the link in the article) is a far stretch by trying to say that "jazz" is Irish, but on the other hand he does have a point that jasm or jism might be Irish when one looks at the sources, which seem to be mostly from New England and the Midwest in America, hardly hotbeds of Caribbean black activity in the 1840s. The dispute as to whether it's of Gaelic, or Germanic, or French origin is probably one that will not be resolved to anyone's satisfaction, though.