As an SS agent it seems likely that this guy had seen the forms before and by all rights should have been able to fill them out in his sleep.
The station chief or another third party called for confirmation but not to the number the agent gave - because he could not confirm it to be an SS office.
The agent got up and left the plane when it was delayed, leaving carry on luggage behind and that luggage included a book in arabic or concerning islam which another passenger and stewardess noted during his absence.
How comfy might you feel sitting next to an abandoned black bag and a copy of "Islam for morons"?
How long before you started to hear it ticking?
How then would you react (as the stew) when you discovered the guy's mandatory paperwork was not kosher?
Finally, aircraft captains share the responsibility and authority of a ship's captain - they get to make the decision when passengers become a problem. Versus - anyone who goes armed into society at society's behest has an obligation to do so with proper respect for the society and not with the arrogance that so often accompanies a badge.
This alone showed he was arrogant. I can't tell you how many times your hear that stupid recording not to leave your luggage unattended.
Plus the SS agent could have made it simple for everyone by stowing his gun. It was his arrogance that he be allowed to carry it that caused the problems. When it became an issue he should have just stowed it.