Clearly, this is "learned behaviour." It's not just the one-finger salute, but the look on the kid's face, the look in his eyes. It's everything.
I don't know who or what to be more frightened of: the kid when he grows up, or the parents and/or people he's been around to "learn" this.
Like a puzzle, all the pieces here fit.
And I don't like what I see.