I can understand well your reaction. I remember back in the early 1990s some pepople from western Europe thought that we, the Polish are one with the Russians. Taking into account that it was the period when we were in the process of liberating ourselves from the soviet regime, it was really offensive to any Pole to be mixed with or taken for a Russian.
Not to offend the Russians, of course. I find them to be very nice people. But the national pride and national animosities in 1980s-early 1990s was the result of the political situation.

so I absolutely understand how it can be to face any ignorance regarding one's nationality etc.