rights are a concept that can only exist in the context of dominant authority; authorities define and enforce rights. it is difficult for me to look at rights from an anarchist perspective, other than to dismiss them. (that of course doesn't preclude the need for anarchists to deal with situations that involve rights, given the world we live in).
i also have a bit of a problem with using "indigenous/native" terminology, but that's for another discussion.
the fact that dominant authorities take over (and largely destroy) land that humans and other life have lived on for generations is of course a massive problem. the fact that there are still humans on this planet that live on land thus far not appropriated by authorities is both inspiring and sad.
but it sounds like you are saying:
i don't believe in rights, but when it comes to "indigenous land rights", maybe i do.
i would simply ask why you hold that particular "right" in some special regard?
the plight of large groups that have been particularly hard hit by the spread of civilization and its paradigm of domination are surely glaring examples of how fucked up shit is. that is a primal driving force for leftist activism. but feeling/showing solidarity - whatever that means to you - with folks you have affinity with is often one of the only things you can do, if you feel like doing something is desired/required.
i lived for 15+ years in an area of the southwestern u.s. that has a largely indian (mosty puebloan, some apache) population. taos pueblo (the closest one to where i was) has a rich history of defending their autonomy; from the raiding apache (and probably other) tribes, and subsequently the spanish and then american colonizers. to this day they retain their own government and laws. the question of "land rights" in that area is, was, and probably always will be a huge conflict, due to the "land grants" that the colonizing spanish issued centuries ago. those grants are the source of constant conflict in the area (in fact all over new mexico), and there are always legal battles being fought around them.