When St. Patrick was coming through Kerry, he had a pet goat, and they killed the goat and ate it. And St. Patrick put a curse on them, that from that day forward, everyone from Kerry would speak in a way that no one would understand and all the other Irish people would laugh at them.
If we ever met an Irish person that we couldn’t understand, we’d always say they were from Kerry.
I think that this is a simple way of building cultural identity. There is a certain anxiety with not being able to understand people that are supposedly ‘from your own homeland’, so they need a reason to justify this, and being that so many Irish people are Catholic, a faux-reigious reason gives it verisimilitude.