Translation:It is not this car that is expensive but that other one.
There are two sentences like this (the other involving a famous actor I think). They both need verbs in the first clause. "It is no this car THAT IS expensive[...]". Reported, but maybe the admins can kill two birds with one stone.
Shouldn't the following sentence be also possible: "This car is not expensive but another one"?
The author is trying to enforce a nuance in meaning which is quite subjective and even eludes native speakers - including me. The whole lesson is pointless.