I'm generally a stickler for the rules, but if in fact the cue ball did barely hit the cue stick I think it's probably better to let it slide.
The story is told of an irascible and very competent snooker referee who was reffing the final frame of a match and the match was down to the final black. Any score or foul at this point ends the match. Player A makes a great shot to pot the black and as the cue ball is still rolling, the referee announces, "Frame and match ...," and the player grabs up the cue ball in triumph, only to have the referee continue "to player B." General consternation and outcry ensued, but the ruling stood.
It is a foul to touch a moving cue ball whether the game ball has been pocketed or not. Many players, even champions, haven't figured that one out. Fouling on a live cue ball in nine ball is the most common overlooked foul. Let the balls stop moving.
So the problem is should the official make a scene in a situation that is of no consequence except when strictly enforced? I think probably not. It would have been interesting if the American in that match had pointed out the foul and demanded another game but I don't think it would have been of much use in the end. It might have resulted in another match or two and would certainly have cemented opinions of the American players in some minds.