Here's the thing with my Polish ancestors;
My great grandfather's family were blond, blue eyed, had names like "Adolph," and spoke fluent German - not Polish. Despite this they always maintained they were Poles. (They were also SHORT. I've seen photos of them next to my Grampa, who barely made the NYPD's 5'6" height requirement.)
My best guess is either they were Silesian, OR decided Poles were a lot more popular in their new country (they came over a little bit before WWI), or possibly both.