Much of this sounds like a joke [1] to me really as the most of the companies I have interviewed with won't tell all this even after signing an NDA. Even asking such questions elicits a strange look (don't you know we cannot disclose what we are working on).

A second question then is why did they ask for an NDA then, and the answer is "company policy". I have refused to sign such NDAs, and they have refused to interview me then.

Interestingly here is something that has worked: I have signed such NDAs with my annotation saying something like "It is mutually understood that this NDA is null and meaningless" right above my signatures, and they do not have any issue with that. Well, as far as I "signed" the NDA per the company policy!

This has been the case with several big name companies I have interviewed with.

[1] Not making fun of you here, rather of the companies and bureaucracy.