First time I heard the phrase it was "Keep your booger hooker off the bang button!" I forget for sure where I first heard it, but it's one of those things I've heard all thru my career.
Regardless, dude shoulda had that thing holstered until it was time to start shooting. Keeping it unloaded or loaded in a holster when you're not on a firing line (yeah, I know he was out in the woods shooting, I'm talking proverbial here) keeps that sort of ND from occuring.