After working in tech for long enough, you realize that no one reads anything, even if its absolutely clear in the UI. And they will blame you for it.
I always have a hard time explaining to people carefully writing pagewalls that throwing out 90% of it would actually be more effective...
At the end it boils down to the truth that a Corporation is a hive mind, an intelligent machine ruthlessly optimizing for stock price and profits at the expense of sometimes human values.
What's not immediately clear is that the video (and channel) now shows up in search results. You won't be aware of that unless you either have a clear mental model of the platform, or try to search for the video title yourself (which implies a certain sort of mental model to be present already).
Sure, people only skim and headline-read articles, but because most articles are shit. That doesn't mean people don't ponder at least a bit when faced with a YT upload page. (And the upload through mobile app is probably more common for non-pro [first time, casual, accidental(!?)] youtubers, there the privacy: public field is pretty visible, legible and explicit.
They can mean anything in people's mind, public is that yeah anyone I send the link can see it, but that's not exactly YT's fault, that people don't make the connection, and somehow live in a fantasy world.
And I cannot blame them too much. People are constantly bombarded with misleading messages (e.g. ads), clickbait stuff, terrible UIs, indecipherable contracts, countless pop-up notification and warnings, opt-out and other "dark patterns".
(disclaimer: personally, I read contracts and agreements and it's often pointless and frustrating)
Due to various cognitive biases most people fail to realize just how big and far reaching that public is.
To share an example from my own experience a few years ago. I wrote a blogpost. I love writing blogs and sharing them with The Public. That's why I write it.
In one of them I used an Xkcd comic. My entire audience, anyone I could ever imagine reading it, knows XKCD and loved it.
But then that blog got 100,000 views. Then 200,000. Then it spiraled. Suddenly I was flamed from all sides, called a disgusting human being and all sorts of things. Why? Because I didn't correctly attribute that XKCD comic.
"Yay my friends and their friends and liek 1000 people saw my thing" is a completely different "public" than when THE public sees your thing. Most people imagine the former when they think "Oh I'm uploading this and it's going to be public"