A non-aboriginal business has licensed the copyright on Australia's aboriginal flag, and are making copyright claims against aboriginal businesses

Are artists supposed to live on air and water? If he can’t sell or lease his work, how can he live? If you want to fix this, don’t wring your hands and say how selfish he is, give the man a decent monthly income for life so he can afford to give away his work. Or the government could arrange a non-exclusive license with him, to provide him some income.

Autochthonous person / non-autochthonous person issues don’t even arise here, really, that’s a red herring. This is the universal issue of who owns an artist’s work.