Law of contract

On Saturday, Chris saw a car in his local garage with a price ticket of $300,000. When he went in to buy it, the garage owner, Frank, laughed and said that the ticket must have been wrongly marked as the actual price of the car was $800,000. However, in the circumstances, he said he would split the difference and let Chris have it for $550,000. Chris asked for time to think about the offer and Frank said he could have three days. Two days later, Chris found out from his friend Larry that he had bought the car from Frank for $700,000.

Explain the contractual implications of the situation to Chris.