I don’t know, but every single one of my parent’s friends and relatives said that when they came to the US.

This labeling often led to some confusing conversations with my grandmother. To her anyone who is not Jewish was of course “Russian”, so whenever I would introduce her to my American friends she would ask if they were Russians (meaning gentiles) whereas I would think she meant “Are they Russian” (as in Russian Jewish immigrants)

It took a while for me to explain this to my (American) wife.

You raise an interesting point, as ethnicity is also often measured in fractions. For my part, I see myself as 100% Australian, despite the provenance of my mother’s family, although I suppose that I can see how people might choose to identify with more than one. Surely, however, that would make them (for example) 100% Australian/Hungarian? Rather than 50% each way? Self-identity is a funny old thing.

Neither Russians nor Russian Jews would call a Jew born in Russia a Russian. It’s just a different worldview, I guess. When Russian Jews (myself included) came to the US in the late ’70s, that was quite an adjustment since everyone called us ‘Russians’.