Sensitive or classified information?
Roughly, yeah. One meaning of 'kuchnia' is "miejsce, w którym opracowuje się szczegóły jakiejś pracy nieujawniane ogółow" (place where details of work/affairs that are not made public are worked out) - also found in the name of an old TV series "Kuchnia Polska" (and the name of a political column in some newspaper some time ago).
sjp.pwn.pl/slowniki/kuchnia.html
In English you might say..... "show how the sausage is made?" "show the man behind the curtain?" "give away trade secrets"?
"Have you"..? for possession is a common mistake among learners. Native speakers of English rarely use it.
I wouldn't call it a grammatical mistake, it's more of a.... stylistic one. It sounds very old fashioned now though it can be heard occasionally, especially in very formal/stuffy situations. I think I heard it in a courtroom scene on tv recently (I forget the series) when the judge asked "Have you any new evidence?" (or something very similar).