The irish are gaels (q celtic speakers), so called from the word “goeddel” or pirate in the brythonic (p celtic) language. The “scots” were a northern irish tribe that invaded and the picts of northwest scotland (p celt speakers) and assimilated them during the middle ages. They are all celts. You are better off dividing your celts in to the ‘q’s and the ‘p’s Q: gaelic speakers (ireland, parts of scotland, man), celt-iberian, maybe lustanian P: Pritani and all brythonic speaking britons, picts, gauls, galatians, and more lately cornish, welsh breton. The greeks were probably referring to p celtic speakers with the word keltoi since they controlled central europe around 300bc.