TSA policy is, when not just arbitrary and capricious — Their actual policy states "TSA officers have the discretion to prohibit any item through the screening checkpoint if they believe it poses a security threat." — it is also the worst possible thing when written. For weapons: if it looks a tiny bit scary, it is prohibited.
They seized a ton of these Star Wars commemorative drink thermal detonators as "grenade like" until there was enough uproar they changed their minds.
Yes. Very very dangerous. Much grenade. And grenades, fake or not, prohibited in even checked luggage.
So, one key part of the story per the TSA is that it was naughty because they should have "declared" the Carl G. But: you can't. There is no procedure to declare a Not Gun. Try to declare and Nerf Blaster and they get mad at you as Not A Gun (look it up: people travel with fake guns for Sci Fi conventions, theatrical productions, etc all the time). No maker, model, serial, caliber etc to put on the form. They actually get MAD at you for wasting their time.
So, best I can tell, TSA had a slow news week and wanted something to show that they get their budget increase for next year. Unless there's something secretly sketchy going on: this was 100% ginned up BS because it looked good in the photo, and TSA is notoriously good at not admitting they messed up and over-riding local stupid decisions so just leaned in