It seems that Microsoft has pulled the new Facebook version from store. If you install Facebook from store now, it will the older version. May be Microsoft was not supposed to push it yet. You can however install Facebook Beta and enjoy the new UI and features.
The stable Facebook version on Windows 10 Mobile has received a major update that takes its version to 10.1. With this update Facebook picks all the new features & UI revamp that we have already seen on new Facebook Beta.
Facebook 10.1 Changelog:
- New visual look
- Ability to see stickers in comments
- New animations while opening and closing pictures
- Support for interactive notifications
- New Lock Screen image look & feel