East, a fairly inexperienced players. was declaring 6NT on the lead of the ♦5.
Upon examining dummy for a few moments, East claimed stating "I've got the top 3 clubs, 5 diamonds, ace-king of hearts and the ace-king of spades for 12 tricks".
North-South quickly accept the claim, at which point dummy (a more experienced player) takes the opportunity to remind his partner that they are playing pairs not teams and he really should have tried for 13 by testing if clubs are 3-3 and then running the diamonds in case someone gets squeezed.
North now contributes to the discussion revealling that whilst he had 4 clubs, the ♠Q was coming down doubleton but it's too late to play for that now.
Dummy opined to north that you can't concede a trick that can't be lost through normal play and if East plays out his cards in the order stated in his claim a 13th trick will automatically emerge. North then called the director.
Who would you rule?
Has dummy over-stepped the mark?

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