Boring technical thing:

Compressed videos have different types of frames -- reference frames (i-frames) and inter-frames (p-frames and b-frames).

A reference frame is a true bitmapped image. Displaying a new bitmap, say, 30 times a second for an hour-long video would take up quite a bit of data, however. So to save space, compression codecs use inter-frames, which are essentially instructions for how to move the pixels from the previous reference frame to create the image in the next frame. The "datamoshing" video effect exploits this technology by artificially removing reference frames, and leaving only inter-frames. The effect is that motion data from later frames will interact with and "move around" existing images.

That's what's happening here, albeit on a very short time scale. This glitchy effect could have resulted from a codec error from the source material or deliberate human manipulation.