Spotify has been working with Facebook for years now and it has also provided the option to log in with your Facebook account. They just recently added the option of Apple ID login and now they are coming up with an option to create an account through Google.
Spotify for Android has now an option of ‘Continue with Google’ option which will allow you to create Spotify account that is connected to your Google account. The existing options for logging in with independent account and with Facebook are still available. There is no account to an existing account to Google as yet.
However you are should stick to creating a regular Spotify account. The Google login button is not available on all of the platforms yet. The only fix will be to convert the account to a regular Spotify login by triggering password reset. Single Sign-On options are also not a very good idea as they can increase the possibility to damage your account if your Google account is compromised. It will result in losing access to the Spotify account as well if your Google account is ever deleted of suspended. This feature is available for Android and the web but is not on iOS or Windows clients. If your Spotify email address is same as your Google email address then you are prompted to login with your email address and password instead. If your Spotify email address is different from your Google email address, you will have to create a new account if you select to sign up with Google.