In June 2015, a United Airlines FFDO threw live ammunition in the trash before eventually deciding to flush it down the lavatory toilet on an international flight from Houston to Munich.
In February 2017, a Southwest Airlines FFDO disembarked a plane in Phoenix, Arizona, leaving a loaded firearm unattended in the cockpit, after the FFDO was accused by a flight attendant of watching footage from a camera hidden in the airplane’s lavatory.
In August 2022, a Delta Air Lines FFDO allegedly used his firearm to assault and intimidate a fellow crew member in response to a possible diversion of the aircraft due to a medical situation.
If I had to guess he either didn’t think it was serious and/or is upset because someone else would take his future route while he’s dealing with the delay.
While a diversion is a PITA for the passengers it usually doesn’t affect the pilot’s schedule significantly. The impact is usually limited to the day of, and the trips are pay-protected. I think the guy just wanted to get home