I assume your bottle had been empty because what you are showing on your video is something I have seen a few times, it is caused by the trapped air between the liner and bottle sides escaping. that only gets there when the bottle is not stored under positive pressure (some air inside)
Stako have said it is a "normal" phenomenon with that bottle because of the way it is constructed and is quite safe.
Personally as much as I appreciate their statement and do in fact believe them, it scares the crap out of me.
Russ