Google uses indexed sites to build up their knowledge graph and semantic understanding of concepts occurring in search, both via explicit JSON-LD semantic tags,

Google uses indexed sites to build up their knowledge graph and semantic understanding of concepts occurring in search, both via explicit JSON-LD semantic tags, and their own inferences. Any feature on google that seems to understand that what you just searched for is a song or a recipe or a company or a person or a movie the data came from some page in the index. Which of course includes lyrics.