Think you need to look up what Racism is mate, being anti Irish could be being a Irishphobe, Anti-Irish, even xenephobia. or the most suitable word is he is a bigot
Race - Each of the major divisions of humankind, having distinct physical characteristics
Racism - Prejudice, discrimination, or antagonism directed against someone of a different race based on the belief that one’s own race is superior.
If he was using Celtic in his insults then yeah he would be being racist mate
He was using Irish in his comments - its a nationality, probably about 90% of people on this forum coming from Liverpool have Irish ancestry but it doesn't make them Irish mate
The idea that the Irish are a race is a utter fabrication, one probably given a lot of credence by the Irish Americans, it is not or never will be a race of people, its a bloody country