There are a lot of product announcements that are handled by uploading private videos that are made public at a given time, so there'd be quite a lot of attacker interest in this exploit if it hadn't been fixed. Worth the bounty.
It isn't a very noteworthy scenario, because it requires the person who _has_ been given access to a private video/ID to share it with someone who shouldn't have access. In that already-rare scenario, the person with access can simply download or record the video anyway, thereby leaking it (with audio and high-resolution to boot). And that's with everything working as intended.
Chained with another exploit to actually be able to discover someone's private video IDs, it would have been worth a much higher bounty.
It is very common for people to discover private video IDs in product pages by combing through the HTML for announcement pages, product listings inadvertently put up early by retailers (and some retailer, somewhere, will always screw it up) etc.
I honestly can't think of a week that goes by without the discovery of a private video ID in the videogame space tbh for some unannounced title or feature.
There are a lot of product announcements that are handled by uploading private videos that are made public at a given time, so there'd be quite a lot of attacker interest in this exploit if it hadn't been fixed. Worth the bounty.