UPDATE: It seems we were fooled, though Android 4.4.3 should be arriving soon, the process does not seem to be unfolding at the moment. Chances are the video was faked or showed an internal device within Google's network.
Twas the night before April Fool's and all the Googlers in the 'plex were preparing their spoofs & shenanigans. Well, except for the hardworking Android folk...
Google appears to be slowly releasing Android 4.4.3 tonight. A Google+ user from Thailand has posted a video of his Nexus 7 (2012) receiving the update. The update, according to Android Police, is expected to carry numerous bug fixes including those for the camera on the Nexus 5 and security fixes, among others. It is meant to be a purely bug fixing update to KitKat.
Android updates are first released to a small subset of people before they are released to the general public. It still may takes weeks before the update is available for everyone over OTA. Currently, the 4.4.3 factory image has yet to be posted for any Nexus device.