They are not that secretive, it's been written about several times. Long story short: a lot of it is still Glenn McDonald, the person behind everynoise, that was acquihired when they bought echonest.
Well, ideally your spotify artist page should contain the genres you're tagged with, along with some info of how that came to be, and even a way to request a change to those. But they don't want people to game the system, and also not let competitors know how they do things (I'm guessing).