He's talking about ethnicity not nationality (Americans are divided by ethnicity such as African america, Indian Americans etc.)
"Ethnicity" is totally irrelevant in his case. His ties to any ethnic group have been irrevocably severed, as I said, and ethnicity requires continuity. He has no "ethnicity". He will never be "Polish" or "Russian" in any sense of the word. He's an American, and that's it. Like many, many other Americans. Actually, I'd be willing to bet that his ancestors were Jewish, rather than Polish or Russian or anything else. Riga and Minsk?