Does this even mean anything? I know there were a bunch of people who received thank-you emails after interviewing and some who didn't; is this similar to that?
It means they haven't decided.
You were told you would get an initial decision within 3-4 weeks of your phone interview (could be a final decision or that you may need to wait longer).
https://www.wdwcollegeprogram.com/sap/its/mimes/zh_wdwcp/students/faqs/faq_notification_process.html
This would be that initial notification. You weren't declined, but you weren't offered either. They need more time to review your application and interview.
December would be the latest you would have to wait. They don't sit on a decision when they make one. So you could really get a final decision anytime before that.