Picture 3 shows the rib on the barrel well centered with respect to the rib on the frame, so the odds of the sight being canted due to barrel clocking are really slim.

Are there a couple of other possible mechanical causes? Yes, the front sight might not be centered on the barrel or the blade of the sight might be bent.

Or, it just may be that the rear sight has to be in that position for the way you shoot that particular revolver. That's one of the reasons they make firearms with adjustable sights. I wouldn't worry about it, enjoy it.