Yes. Basically you're confusing the two pages. That second screen isn't the Login screen, it's the create-a-new-account screen. You didn't reload the login screen, you got taken to a new screen.
The Register page looks similar to the Login page, but it's not the same thing. When you get to the page that says Username and Email, then that's you creating an account. This will happen after the FB popup goes away. It should fill in your name and email on that page, then all you have to do is to click the Register button, or change the username you want to have on the site and then click Register.
You can't log into the site without an account on the site, so you have to create that account. The SFC-Register plugin helps you do that by filling in the email address and name and such, but you still have to create the account.
However, one benefit of creating an account using the FB login is that in the process of the account creation, the new WP account will be automatically linked to the FB account. So you'll then be able to login just by clicking the FB Connect button.
Essentially, when you click the FB Connect button, first it looks for any existing WP accounts already on the system that are connected to the FB account you log in as. If it finds one, then it just logs you in. If it doesn't find one, and you have registration enabled, then the SFC-Register plugin takes over and sends you to the page where you can create the new WP account, which will be then connected to the FB account.