Because the concept of ownership did not exist, there could be no rightful owners. I get your logic. It is just completely flawed. The second the land was taken, the European concept was introduced, and injustice took place. The land was seen by those introducing the concept of land ownership as the indigenous people's land. And, theirs for the taking. Taking!
Because they had a different concept of ownership, or no concept at all, the land is forfeit. False.
So, there was an earlier genocide against the blacks in SA, which is being corrected. I see no problem.