Also, apparently he told this to a flight attendant, not the TSA. While this type of highjacking seems a bit passé now, this would be a pretty typical start to a highjacking fifty or sixty years ago before directing the plane to Havana or Tripoli.
Playing "devil's advocate" here it is possible a person who is insane might say something like that. And if the TSA is going to catch anyone it is not going to be the reincarnation of Carlos the Jackal, but rather a Richard Reid doppelgänger.
It is also notable that he is being charged under Florida Statute § 790.164(1). Indeed, it could also be a far more serious federal crime: 18 U.S. Code § 35 describes an offense by which anyone who willfully and maliciously, or with reckless disregard for human safety, imparts, conveys, or causes false information to be conveyed, knowing the information is false, related to an attempt, or alleged attempt being made. That is before looking into what I image are a panoply of laws about interfering with anything near an airliner.
