No, but they expect the value to be a certain amount in 3 years time. If a lot of consumers jump on this and a majority of them jump on the next 3 year contract after that then there's going to be way more used cars on the market in 3 years time than initially expected, causing values to collapse. You don't have to assume a rising value in order to have a bubble.

It is true however that it's a really small market compared to housing, car companies also aren't critical to the economy as a whole in the way banks are but it would still be bad.