I don't call myself English because I am a mix of lots of things, including Dutch, Portuguese, Scottish, Irish and Hungarian. I speak English, I was born in England, but my nationality is British. My ethnicity is a bit muddled up, but my nationality is British. A person born in Australia who qualifies for that nationality is Australian, but they might feel their ethnicity to be completely different. They might answer Italian or Greek of Indian or anything else in respect of ethnicity and that is really the point I am making ;nationality and ethnicity can be different and that might be where this person is coming from.
I am not making an apology on behalf of this person for bad manners BTW just offering an explanation of how they might think.