No. They were looking at the teeth themselves, morphologically, not at DNA from those teeth.
They found that teeth from homo antecessor did not closely enough match our own to be considered -- in their opinions -- as common ancestors with Neanderthals.
I'd say that's fine, since the truth of the matter seems to be highly complicated, and may-or-may-not directly include homo antecessors.
So this study simply tells us that science is still a long way off from finding definitive answers.
I remembered the 20 percent number from somewhere, and probably got it wrong. iT IS heck getting old.
my apologies.