It might be a bit difficult for the highly technical HN crowd to grasp how little many people understand technology. Not changing the title is already a big clue. Since it was a feature built-in to a native app, people might have thought their videos would not be public or only shared with friends, and lots of them might not even have understood what they were doing at all.
It might have been "published" to YouTube, but was it really done so with informed consent?
This is unlikely to be a popular opinion here, but mass downloading of IMG_0001 videos is essentially trawling for private data by looking for an identifier of accidentally unsecured private data, akin to searching for "{ apiKey: " in github.