Could this be the same Hugh Cassidy mentioned in relation to the Macken Fight? Unlikely given his age. Perhaps the family story is a bit confused? Perhaps Owen (this Hugh's father) may also have had a brother named Hugh and the reference was for him, although the death certificate suggests otherwise?
↑ Paternal relationship is confirmed through Y-chromosome DNA testing. Cassidy-453 and Cassidy-1188 match on 35 out of 37 markers (see YSearch IDs 9EJCS and ZQYVC) thereby confirming their relationship as fifth cousins and their direct paternal lines back to their MRCA as yet Unnamed CASSIDY.
It may be possible to confirm family relationships with Hugh by comparing test results with other carriers of his Y-chromosome or his mother's mitochondrial DNA.
Y-chromosome DNA test-takers in his direct paternal line on WikiTree: