As Gabe Aul points out in the build’s blog post, this release follows from the Development Branch, which provides builds first to devices that shipped with Windows 10 Mobile. Those devices include the Lumia 950, 950 XL, 550, and the Xiomi Mi4.
Today, we are releasing Windows 10 Mobile Insider Preview Build 14267 to Windows Insiders in the Fast ring. While we have been releasing preview builds for PC from our development branch for a while now, this is our first new preview build for Windows 10 Mobile from our Development Branch this year. As I mentioned a couple of weeks ago, initially we’ll make new builds from our Development Branch available only to devices that shipped with Windows 10 Mobile. Currently this includes the Lumia 950, 950 XL, 550, and Xiaomi Mi4. We plan to expand from there as we release Windows 10 Mobile to other devices.