The wording of this answer is tricky. I interpreted the correct answer in two ways:

When the director "could not properly infer", the idea did not occur to him, and thus he did not make the inference. This reminds me of like a logic game: oh, i got this wrong because I "could not properly infer" that A and B have to be next to each other. Contrast with somebody who "could properly infer"; they would have made the inference.

When the director "could not properly infer", it was not proper of him to make the inference, even though he did. There's no situation here where someone "could properly infer" because the inference itself is improper.

I think people are more likely to speak in the way described in my first interpretation, though this question requires us to adopt the second interpretation. Honestly, I think this question kind of stinks because it's uses an expression in a way that we normally wouldn't.

B is not correct because the political advisor's reasons are not advancing free speech "for its own sake". Their argument is based on the positive benefits of free speech. The argument would have to be totally different if it was advocating free speech for the sake of free speech i.e. humans have inalienable rights to speak their mind or something more essential to humans and rights.