He was never in the Service, He is not in the Chain of Command, and he is not "Under arm's" (Wearing a hat for the Civ's )
So He is doing the "Right" thing .
And as the only Civilian he is a bigger sore thumb than if he were screwing up

(We might be underestimating Joe "Quayle" )
Secret Service is working, requiring them to salute the Flag would produce a predictable time when everyone's hands would be about as far from their weapons as possible, that would be a vulnerability.
It's a joke people!
I understand that it's a joke Headline, and I did laugh, but I'm commenting just on the photo which I assume is real.
Joe may find himself facing RE Lee's question ?