At he turn of the 1900's, what is today's Poland was either Germany, Russia or Austria-Hungary. There was a lot of economic immigration of ethnic Poles from the Galicia area of Austria-Hungary into the US at that time. I think I read that area had the most emigration. So that post has some history to back it up, IMO.
The Austrians let them be autonomous, for the most part; they didn't disrupt their culture. That would mean they were technically Austrian citizens, but kept their language. I have no idea under what passport they emigrated, with.
That area would be the Western part of Ukraine and the Southeastern part of Poland Today.