To be fair (and more exact) Spotify data scientists detect patterns in the audio spectral features and use them to manually create/add new genres. The "collective wisdom" nature of last.fm and RYM will often give better results/phraseology.
You could say that Spotify could also be data mining these Music Social Media sites!
My own research does not show this to be true (at a large scale anyway). But they should (and pay them for it)
I mean, I'm pretty sure it is not just audio spectral features used, though I can't find a citation either way. (I am sure because the language distinctions make clear that we are at least making heavy use of metadata if not actual social patterns in listening, but the latter is explicitly heavily used elsewhere on the site, so...)
Also, if we're being exact, it's the work of Glenn McDonald under the auspices the Echo Nest, which is now owned by Spotify, but it isn't the be-all-end-all of how Spotify models genres under the hood.
What I was curious about is how /u/beezlebroxxxxxx perceived it to do at the metal genres, simply because Glenn McDonald is himself a metal genre fan (https://www.furia.com/), so I'd've expected that to work decently well.
