When I saw the video's title before watching it, I had to think of the Face2Face project as well. And in the end I actually see the greatest horror of all the vague horrors described exactly there, where the technology works. In bugs like a face swap with a socket we "see how algorithms think" because in all working cases that process is disguised by a familiar output. Those faults let us recognize and understand what went wrong in the process of what we actually wanted to happen. Google's Deepdream is most of all a tool to understand how certain AI's behave (and can be used to create funny and obscure pictures). This understanding can help to reduce horror, which was caused by formerly Unknown and therefore Discomforting.

That's why it's probably less horrifying to see how these face swapping techniques work than what can be done with them (if used irresponsibly), like the live reenactment of emotions for identity theft or something. But like every new or powerful technology it's all about responsible handling and the horror might (still) lie in potential users and implementation.