They want that to be recognised in a similar way to how the Maori were recognised in New Zealand.
States and nationalities =/= ethnicities. Someone can be an American by being a citizen of that country, past or present. Someone can be Californian by being a resident of that state, past or present. Someone is Aboriginal Australian by virtue of being born to another Aboriginal Australian. Nation states and ethnic identities are utterly different concepts. When I fill in a government form, I am a UK citizen, and identify as a British person; not as any of the other multiple options available to me. There are two separate boxes. I can become a US citizen, or a Canadian citizen, or a Mexican citizen, and identify with that nationality. I can't decide one day to become an Arab or Gypsy ethnicity, even if I lived on the Arabian peninsula or replaced my car with a horse and trap.
That's an advisory body based on genetic traits that manifest superficial changes, that's what I was responding to. You're right that you can obtain a nationality but not an ethnicity. That's why I explained that you shouldn't think of it as ethnicity but closer to nationality.
Look at the beginnings of Australia. Would you think it odd if the colonial government had decided to somehow recognise the current inhabitants of the land?
Given that they didn't and instead committed various atrocities, why do you think it's wrong to retroactively recognise the affected people? The people today in our reality are just as descended from the people from then as the people of the fantasy land.