To understand this concept a bit more allow me to go into some details,
Scanning an entire video for bad shit = costly
Meta obviously does want to make sure no celebs or bad stuff is spotted in the video but at the same time does not want to spend even more money and go through several minutes of video ads with 100+ being uploaded which would be a huge loss in money for FB.
Instead, they kinda scan the obvious, which is the first 10 seconds.
To view entire videos manually it's going to cost even more, which AI is replacing at the moment.
Back in the day, even Images that did well on BH would get scanned and almost automatically banned so what we did back then was re-compress the image or simply add a pattern or layer over it in Photoshop or whatever and set it to a 1% Opacity, so the image would not be automatically flagged.
With videos, it's also encrypting and compressing but adding a few seconds of a clock video before the real video starts does help as well, but I am not a huge video tech so someone else is probably able to explain it much better.
Pretty much what everyone already said, it's just to fool facebook.
IMO this way is not that effective tho, though I believe people with video skills know how to plat with the data of the video.