I'll go out on a limb here and say that if you have a gap between two balls and want to hit a third between them, it is impossible to hit the far ball first and move both of the "gap" balls.
Maybe, contrary to what I claim above, it is barely possible to move both of the gap balls, but if so, I suspect that only minor movement of the second gap ball struck is possible. In the actual shot (as I recall the live event -- I have not seen the video) both gap balls moved a lot.
As I recall the shot, the 8 was farther from the gap balls than the illustration above. Would someone who has access to the video check this?