In case you weren't aware, yes, Irish is an ethnicity, dating back over 9,000 years, making it older than most existing ethnicities. Wikipedia has more information: https://en.wikipedia.org/wiki/Irish_people

Being an island, Ireland was quite cut off genetically from the world for quite a long time, allowing a distinct ethnicity to develop. And as you may be aware, "race" isn't a real scientifically valid concept, but the word is used colloquially to refer to ethnicity, which is a scientifically valid concept that can be measured using genetics.