Answer:
mutual mistake
Step-by-step explanation:
A mutual mistake happens when all the parties involved in a contract (two or more) are mistaken or do not know the correct information about some specific material fact that is relevant to the contract. In this case, the contract can be rescinded because Harry believes that Ryan wants to buy his Cadillac, while Ryan believes Harry is selling his Porsche.
Since both of them are mistaken and do not know relevant material facts regarding the contract, the contract can be terminated.