They have programmed it seemingly to me to imitate gaming textures in 3D games or skins if you prefer that term. They likely need a video with a person of similar head shape and size and just add the skin and have a bunch of scripts to allow it to know where to place the nose and such and how they are normally shaded also. It's a lot of stuff but a person that gathers enough of the video editing knowledge and 3D knowledge combines this doesn't seem like an impossible feat. It mostly takes time and talent. It's not really AI but an automated programs. If it doesn't make all it's own decisions and learn to improve itself I don't consider it AI more like a robotic program that is fully featured.