As long as I could remember, the Price Is Right gave away new cars and merchandise.
The woman who won this Mustang was very excited. I would venture to say, she probably could not tell the difference between the different Mustang models.
It is a well established fact a standard Mach 1 has a higher value than a standard convertible.
Image her dismay when she finds out that the car she won was a fake. This would no different than if she had won a Rolex only to discover what she won was a cheap street corner knock off.
So, yes this is a joke and a cruel one at that. Unless the Price Is Right provided documentation listing her winnings as a regular Mustang convertible, not a Mach 1 convertible, they could be sued for fraud.