There are a lot of ways information about new phones and phone software can leak, which is why they're so prevalent.
What isn't as common is a company accidentally leaking its own stuff, but it happens.
Case in point, Google seems to have accidentally revealed that Android P will have gesture controls similar to those found on the iPhone X.
But obviously better because it's being done by Google and not Apple.
Over on the Android Developer's Blog, Google announced that the Android P Developer's Preview would be prioritising DNS over TLP, which is a technical network security improvement that nobody cares about unless they're a developer or a huge nerd (possibly both).
But the original blog post came with a little extra, in the form of a screenshot that seemingly displayed a brand new type of navigation menu.