How it works

A Google search is not simply a raw dump of a database query to the user's screen. The retrieval of the data is just one step, there is much post-processing afterwards, in terms of presentation and customization.
When Google "removes" material, often it is still in the Google index itself. But the post-processing has removed it from any results shown to the user. This system can be applied, for quality reasons, to remove sites which "spam" the search engine. And that is, by volume, certainly the overwhelming application of the mechanism. But it can also be directed against sites which have been prohibited for government-based reasons.
Sometimes the fact that the "removed" material is still in the index can be inferred