This conclusion would be incorrect only if there's evidence that some of the other hominids was burying the dead before the Homo neanderthalensis.
In order to have such a claim, the anthropologist will have to have a proof that will confirm that the burial sites of the Homo neanderthalensis are older than the burial sites of any other hominid species. If that is not the case, and there's proof that some of the other hominids have been burying their dead before the Homo neanderthalensis, than the claim will be wrong.
Also, it is very tricky to make a claim like that, because the fossils of the hominids are pretty rare, and that can be a clue that they have been burying the dead since they are so hard to find even though they have all lived until very recently (geologically speaking).
