Answer:
S’s claim that mistake was mutual is false.
Step-by-step explanation:
The Seller’s claim that the mistake was mutual is not correct as the seller has incentive to mislead the facts after learning the new information about the property and substantial rise in its value.
The mutual mistake is happens when there is fundamental disagreement about the material aspects of the contract. But that is not the case here as both buyer and seller agreed about the same price of $15,000 and sale of the property is completed before getting the new information, although its worth was only $5000.
Therefore it is not the case of mutual mistake and S’s claim that mistake was mutual is false.