Answer:
Donald's claim may not be correct.
In this case, Donald made an offer with a stipulation that the offer would expire on February 4th. Dwayne made changes to the offer, which created a counteroffer. Donald did not accept the counteroffer until February 18th, which was after the date stipulated in the original offer.
Dwayne had the right to terminate the negotiations on February 14th, as Donald did not accept the counteroffer until February 18th. Therefore, the negotiations between Donald and Dwayne were terminated when Dwayne sold the property to someone else.
However, it would depend on the specific terms of the offer and counteroffer as well as the laws of the jurisdiction in which the contract was made.