On the slow motion video part (when their logo was flopping around, lol) it looked like the BCG slides back, STAYS BACK for a considerable amount of time (so it's being jammed to the rear REALLY hard to stick like that), then moving back forward.
Here's a video of the AK in one of its original calibers in slow motion. While it still has some stop at the rear, no where near the bolt hang time as the .458...: https://www.youtube.com/watch?v=HGivoWD9OvQ