Shamelessly stolen from you-know-where.
Commenting before reading other comments
Solution to grid puzzle
The henchmen's discussion implies that the letter row and number column both have at least two balls in them (required for "I don't know, but I know you don't know)". Bernard's statement to Albert makes it clear to Albert that the letter must be either row C or D depending on the number he knows.
If it was row D the answer would still be ambiguous to Bernard so it must be C3 and the ball is gold
Solution to overall puzzle
I've been successfully nerd sniped and my family is dead.