It's a pretty big stretch to say that "the Irish" refers to the prehistoric inhabitants of Ireland that we know very little about and not the Celts, who forged a distinctive national identity and culture and maintained it for thousands of years. It's true that the Celts weren't the first inhabitants of Ireland, but very few ethnic groups were the first inhabitants of the nations they now identify with. For example, Anglo-Saxons are usually seen as being quintessentially English, but they have far less historical claim to Britain than the Celts do to Ireland.