Hmm, I thought the shot should be restored, but looking more carefully at the rules, maybe not. Rules 1.7 and 1.9 seem to dance around the issue but don't quite cover it:
1.7 Balls Settling
A ball may settle slightly after it appears to have stopped, possibly due to slight imperfections in the ball or the table. Unless this causes a ball to fall into a pocket, it is considered a normal hazard of play, and the ball will not be moved back. If a ball falls into a pocket as the result of such settling, it is restored as closely as possible to its original position. If a settling ball falls into a pocket during or just prior to a shot, and this has an effect on the shot, the referee will restore the position and the shot will be replayed. The shooter is not penalized for shooting while a ball is settling. See also 8.3 Ball Pocketed.
1.9 Outside Interference
When outside interference occurs during a shot that has an effect on the outcome of that shot, the referee will restore the balls to the positions they had before the shot, and the shot will be replayed. If the interference had no effect on the shot, the referee will restore the disturbed balls and play will continue. If the balls cannot be restored to their original positions, the situation is handled like a stalemate.
Rule 1.7 doesn't quite apply because the 8-ball didn't fall into the pocket when it moved. Rule 1.9 would only apply if you could argue that "outside interference" caused the 8-ball to move, not "settling". Either way, I think the "spirit of the rules" calls for restoring the balls and letting you shoot again, but maybe I'm grasping at straws.....