It says quite clearly: "Log in with Facebook or Spotify". That means you can log in using a Facebook account or a Spotify account.
The username field says "Facebook Email or Spotify Username". So when you type an email, you log in using a Facebook account.
It's not that hard to understand. By the way, that account you made on the sign up page is still unused: you logged in using a Facebook account, which is a different account from the one you just registered, so you have two spotify users now - one you signed up w/o Facebook and one you actually logged into.
It says "Log in with Facebook or Spotify," not "Log in with Spotify, or log in with Facebook, reactivating a disabled account if necessary, and then grant us a bunch of permissions." Nobody cares that it attempted a Facebook authentication. We care that it silently reactivated the Facebook account and silently gave itself permissions.
I disagree that it's clear. A placeholder in a field is no substitute for an actual label. It should be an enhancement, not a replacement. With the number of places using e-mail addresses as usernames, it's a natural mistake.
The username field says "Facebook Email or Spotify Username". So when you type an email, you log in using a Facebook account.
It's not that hard to understand. By the way, that account you made on the sign up page is still unused: you logged in using a Facebook account, which is a different account from the one you just registered, so you have two spotify users now - one you signed up w/o Facebook and one you actually logged into.