Not quite so simple. I guess that the above only applies if you live in a country where it is easy to assimilate into a "dominant" ethnicity/race. If i were to move to China, and had children with a Polish woman, and so did their children, and their children, etc., do you think those grandchildren would be called Chinese? No. They may find themselves with Chinese citizenship, but no-one would call them "Chinese". It also depends on whether "nationality" is more important than ethnicity or race - none of these are the same thing.
Over here, as it is still quite easy to "hide" yourself within the British population as a Pole, it's possible for people of Polish ethnicity to claim to be "English", and no-one will know. My sister is one of those people - she can't speak a word of the language, has nothing to do with Poles except for close family, despises Polish people generally, and calls herself "English".
I, on the other hand, have always maintained contact with Polish family, speak the language fluently, and am very aware of my origins. Both of us were born in the UK. I call myself Polish, but I am also very proud to have been born in England, and will never hide or deny this fact. I never call myself English, but I have no problem calling myself British (despite the fact that our recent Government would like us to feel ashamed of this, lol). But none of this changes the fact that I am simply NOT ENGLISH.
I suppose the test could be: what would a Nazi-style person or organisation class you as, if they used every medium possible to find out who was really who? In my case, I'd be up against the wall (as would my sister, lol) as we are clearly very ethnically Polish!
I mean where did the Poles originally come from? Central Asia?
Considering how much R1a DNA we share with Brahmin Indians, that's more accurate than you think! Why do you think Poles think they are so superior, lol ;)