I'm not sure you'd want to involve NLP. I think it's more down to the fact that it's relatively easy to reverse engineer the function generating the question and get the parameters that way.

Wolfram Alpha won't answer very many questions of that sort[0] but a cracker can spent a couple of hourse to enumerate all kinds of questions and writing tailored functions (and a detection routine) for each. If your detection routine is naive (e.g. choose randomly) and some or all of your answering functions work badly, no problem, you only have to get it right occasionally anyway.

[0] And indeed it fails unsurprisingly if comically for the second question How many times does the word four appear within this sentence?, trimming it to How many times and showing details about the British newspaper.