I actually followed the story a couple days ago. So, are you saying it was not prohibited for him to enter airport property with a gun? I know they can be checked in when one is flying. But, there are probably regulations on how they are carried. According the PD a couple of days ago he was meeting someone at the airport.
I believe you can carry a gun (concealed with a permit) right up to the security checks - which you cannot go beyond without a ticket. There is nothing illegal about carrying a concealed weapon all over the airport, as long as you are on the non-passenger side of the TSA checkpoints. Happens every day and happens every time I go to the airport when I’m not traveling.