He concludes that she has a hearing problem. So he decides to conduct a hearing test without telling her about it. Still no answer. He moves still closer and whispers the same words, but still no reply. But when he tested them out, the Spirit of truth speaking through the voice of his wife informed him otherwise.
Truth is more than just gathering facts.
It also means conforming to reality. The reality for the husband was that he was the one with the hearing problem. It took his wife's words to prove it. What this verse suggests is that all human judgments must square with God's if they are to know what is true. Truth for Christians must be more than the collection and recording of facts.