Its just a protocol that integrates Ubuntu and Android. As far as the video goes, Ubuntu is not running on the phone or Android...but the features from the phone are supported within Ubuntu.
This is not an Ubuntu app running atop Android, nor it is an Ubuntu device running an Android emulator. Rather, Ubuntu for Android is a full Ubuntu desktop running side-by-side with Android on the same phone.
Ubuntu for Android provides a full desktop experience, including office software, web browsing, email and media applications, on Android phones docked to a screen and keyboard.