If Saint Patrick's parents are Italian why is he Irish?

Saint Patrick's parents, Calphurnius and Conchessa, were Roman citizens living in Britain. Patrick's father was a high Roman diplomat.

Britain was part of the Roman Empire at the time. Saint Patrick was kidnapped and sold into slavery and taken to Ireland. He escaped and went back to Ireland after becoming a priest and was determined to convert the nation. St. Patrick adopted the land of Ireland when he went back there to preach, and they adopted him as their national saint. You might say that he was a naturalized citizen, which is why he is considered Irish.