I am having difficulty understanding anything at all presented in the question.
(A) I do not know what the phrase "question tag" means
(B) I could discuss "naturalistic intelligence" in the context of Scientific Data, but you have not shown that your source is a Scietific source. It does matter who writes the claim, because not all persons are clear on the meaning of "naturalistic" or "intelligence".
(C) I can understand the use of "Don't they" as an answer, but there is a difficulty here, because although I can understand your answer and accept it as an answer with a slightly sarcastic "edge," your instructor or teacher demands an absolute grammatical perfection.
That would be a problem for you and for me, because few Americans as Native Speakers would quibble over the difference. Perhaps relevant also is the fact that your instructor employs a CONTRACTION in a written context. Contractions are appropriate to speech, but arguably, not to writing as text, and especially not appropriate to academic writing.
So we can complain about your instructors correction, but our complaint probably will not be heard. Petty criticisms like "haven't they?" occur in academia.