MicroBalrog,
He had left his jacket in his car, and was open-carrying in the small of his back. Where he couldn't see the gun, but everyone else could.
I suggest you ask any firearms instructor if that's wise.
The fact that the officer was able to sneak up behind him and grab the gun, to me, demonstrated that that's not a particularly safe way to open carry, and that he ought to have been grateful that it was a cop, not a bad guy who did that.
If you are going to open carry, at least have the gun in your sight and/or in your immediate control, not somewhere where you can't see it, where everyone else can, and where you'd immediately lose retention of the weapon in a surprise grapple.