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.