The article talks about Neanderthals and Homo Sapiens as being separate species...
Yet, it also mentions how Neanderthals got assimilated into the Homo Sapiens community. To assimilate means that they reproduced across the species. If so, they were not different species. Neanderthals and Homo Sapiens were as different as blacks and whites of today; they marry and reproduce across color lines, meaning that they were/are all of the same species.
I think in this case interbreeding species to create “Mules” might come to mind as a comparison?