I agree. Flynn knew by the questions they were asking him that they had already been listening. He told the truth. They couldn't find anything on him so they faked it. He seized the opportunity as a master strategist to plead guilty to a BS charge, knowing nothing would happen. He was released from his NDA and could then dump info on everything he knows when the SC got to him.
FBI guy I know says they never bother with the old "lied to the FBI" charge. Says that the judge will never sign off on it. "That's all you got? No. Cut him loose."