A moral cul-de-sac
Whether that assertion was actually made or not, it is still widely believed both internally and externally that Ireland is indeed such a country and, that being so, there can or should be little or no surprise in hearing it said.
However, saying that “this is a Catholic country” is different to saying “this is a country where Catholicism is the dominant religion” or “this is a country where Catholicism is the religion of the vast majority of the citizens”.