Is it considered a lie for a person to say "I don't know" or to answer incorrectly when asked about their personal secrets or their family's secrets, in order to avoid interference in their private affairs?

If a person is asked about private matters that he knows, his saying: "I don't know" is a lie that is impermissible. Euphemisms can be used, such as: "Allah knows best," or one can refrain from answering, as the question is not originally obligatory. It is mentioned that "part of the perfection of a person's Islam is his leaving that which does not concern him."