It was a joke about the feature of the same name in the context of regular expressions.

They'll ask a series of incriminating questions resulting in negative answers from you that can then be shown later to be false by inference. They may get you to assert that you never been to a certain location or never taken a certain action, they will accept that assertion, and then get you to add details to it. Later they'll show that one of your assertions was false, and therefore, all of the other dependent ones must be as well.