The green icon appears if your database is unlocked. It doesn't tell if you have credentials for the site or not. The popup shows an icon with a questionmark if credentials are found, and the same feature will be implemented to the Username field icon later.

If you have troubles for getting your credentials to the site, please ensure your entry URL's are correct. Sometimes pages use iframes from other subdomains for the login fields, so the safest best is to use https://example.com instead of https://loginpage.example.com. When a subdomain is removed from the entry URL it works as a wildcard, meaning https://example.com will match https://*.example.com and so on.