The US is also a Protestant nation, yet there are Catholics here. When people say a country is a nation of a particular religion, they mean a particular religion is dominant. In the US, we used to talk about WASPs because the most privileged people tended to be White Anglo-Saxon Protestants.

Are you arguing that Israel is not a Jewish nation because it includes some Muslims?

And are you arguing that the German-Americans who were interned during WW2 were Catholics?