It's using similarity search[0]. You transform audio files into vectors using some embedding model like vggish[1], then index those vectors. Then turn the query audio file into a vector the same way, and search the index for vectors similar to your query.
Full disclosure: I work for Pinecone, which provides similarity search as a service... Including for audio data.
Full disclosure: I work for Pinecone, which provides similarity search as a service... Including for audio data.
[0] https://www.pinecone.io/learn/what-is-similarity-search/
[1] https://tfhub.dev/google/vggish/1