I'd much rather be surrounded by people wearing earbuds than have people watching tiktoks through their phone speakers on the subway
That just sounds like another version of what the author is talking about: using [device] to avoid human interaction.
It's essentially the same unspoken etiquette rule as what you're socially expected to do if riding a crowded elevator.
Go commute by NYC subway 10 times a week, M-F especially during peak tourist season and you'll understand.
I intentionally behave completely different if I'm in a small town of 3000 people or walking down the street, shopping, riding transit in a large city.