This is only kind of true. If you are asked "why is X true?" and you go on critique the epistemological basis for saying that something of type X could be true or not, you may be giving an in-depth and intelligent answer that is responsive to the prompt. But you are also not demonstrating the knowledge that the question was designed to probe; i.e., that you have learned and retained the particular arguments for the truth of X that were covered in class.
These discussions sometimes go off the rail because it's a bunch of STEM folks critiquing the humanities, so I'll share a STEM example that gets the point across. A too-clever friend of mine got marks off in our Analysis course because he presented a constructive proof of a theorem on a test, and that was not the proof technique that the test was designed to interrogate.
Superficially his answer was "correct". But then, as his professor pointed out, on an even deeper level it really was incorrect, because our write-ups of proofs are really high-level descriptions of formal derivations, and the student was describing a proof a different axiomatic system than the one assumed by the question, so, to be totally correct, he would have had to embed the proof that his proof in constructive analysis mapped over into normal analysis. Which would have been quite a bit of work that the student, at the time, was unable to do (and probably no one could do in an exam setting).
But, again, the real point is that this part of the debate is pedantic because what my clever "friend" really didn't understand was WHY the question was being asked. The answer is supposed to demonstrate a certain piece of knowledge in a certain context; it's an exam answer in a closed curriculum, not a Treatise.
Besides, you are ALWAYS writing into a audience and context; if you want to write to a "pure" audience, you may do so, but consider saving it for Sunday morning prayers.
Which, since that friend isn't paid to write analysis proofs these days, were perhaps important lessons ;)