Seems there can only really be two trains of thought:
* if you don't believe the sound in the video is the RAT, then it has to be a flaps retraction mistake
* if you do believe the sound in the video is the RAT, then it has to be dual engine failure (with whatever cause).
IMHO, I do believe quite firmly the sound heard in the higher-res video is indeed the RAT, and that the other sound will be a combination of drag noise (gear and flaps out, remember) plus the engines windmilling. They do not sound like GEnx engines on full chat.