Looks like some lucky (or unlucky) guy got himself a test build of Key Lime Pie instead of standard KitKat on his new Nexus 5. Upon firing up his Nexus 5 (which was purchased second hand), he noticed it was unstable and kept crashing. Inside the Settings menu, he found this:
It’s a test version of Key Lime Pie, Hammerhead codename for the Nexus 5 and all. Many of us would consider him very lucky, but having a constantly crashing device is no fun. There were a few hidden menus enabled, but nothing exciting or inaccessible in the regular build. No goodies to be found here, unfortunately.
It’s not uncommon for devices to ship with an old build of Android, but they’re updated when they’re started. However, test builds do not receive OTA updates like normal builds do, so this user had to flash a KitKat image on his device. While a hardship, it offered a peek at an early Android build and is simply a cool little story.