No-one who claims to know Thing One about St. Patrick thinks that he was Irish; his non-Irish origin is a fundamental part of his story. I've never understood the perennial sputtering about him "not even being Irish" as if this is some sort of revelation. It's not. The story of St. Patrick is predicated on his not being Irish.

Corned beef, on the other hand, is a real myth; an American substitution for the traditional joint of bacon (smoked pork loin or shoulder).