It's simple and how LE interrogates. They keep asking the same question over and over and if a suspect says just one word wrong, they may have committed perjury. Plus, it now appears that if Flynn didn't plead guilty to perjury, the FBI was going after his son.
NEVER EVER TALK TO LAW ENFORCEMENT WITHOUT AN ATTORNEY PRESENT! All you need tell them is you refuse to say anything without an attorney present. However, you can also use the Hillary protocol of, "I don't remember"; "I don't have any recollection of that"; "I can't recall"; "I have no memory of that". There is no way anyone can prove you don't remember, unless an eye witness or documents prove otherwise.
Or alternate theory:
He intentionally plead guilty to force the release of incriminating evidence against the derps, as we saw yesterday and will see again tomorrow.
How do you get evidence into the legal system and the public domain?