No, Facebook didn't sell them the data... they gave it to them... sort of. CA made a personality test, got users to take the test and grant them permission to use their Facebook data. So users gave CA the data. But, the data users gave CA also included data about their friend graph. CA apparently did not reveal what they were going to do with the data. It was also against Facevook ToS to use the social graph data this way. But CA did it anyway. So Facebook did not sell it to them, they just had an API that have the data away. In the wake of the CA scandel, Facebook shut down parts of their API that allowed this data to be obtained.

CA used a large variety of timewaster Facebook apps (Quizzes and the sort) to gain access to more user data than was likely ever intended, not just about the party that authorized the app, but also about their friends. They essentially extracted the entire social graph including likes and did all their extrapolation from there.

It is more Facebooks inaction despite being aware of this rather than their actions.