Agree with LP here.

Players now (since the new 2008 rules were intro'd) must ID their ball before playing it from a hazard.

If you are unsure a ball in a bunker is yours because it is buried and your ID markings are not clearly evident, you are allowed to mark the ball (advising your marker or opponent of what you are going to do ahead of time), clear away as much sand as is required to ID the ball, you must then attempt to recreate your lie as best you can, then go ahead and play your shot.

The fact that your opponent advised your partner which ball was which is pretty much irrelevant, the onus rests with the player to ID his own ball.

__________________
Look at the Target, Look at the Ball, Swing... Dr Bob Rotella...