>I'm a Notre Dame fan because I'm 'Irish'
>I'm a fan of '_________' because they were good when I was a kid
That article is wrong, the name comes from an Irish immigrant who fought in the Civil War and then became president (or maybe chaplain?) of the school. He was a "fighting Irish" and was the representative of the school so that became their moniker.
The article does have a point though, Catholics/Irish people in the US were probably the most hated ethnoreligious group other than blacks for an extremely long time. Catholic churches would be bombed, members lynched by the KKK etc. There was a tendency to generalize all Catholics as Irish so it makes sense
>I'm a fan of a team because I just so happened to be born near where they play