Google has been doing this for ages, not only with Books results but web search results. If the query is associated with some Entity, it will return various (hopefully useful) about that entity even if they do not contain text involved at all.

This is how, for example the query "that movie where there are two magicians" returns varied results about The Prestige, whereas "that movie where there are four magicians" returns various results about Now You See Me.

A pure text search would likely return very similar results, but the entity mapping heavily impacts the search results.