He was posting to his network of friends/subscribers and the columnist grabbed the thread and decided to show it to the world. Twitter is an odd medium, most people's audience is their friends, but then it is also a public forum. Like having a conversation through a megaphone in a crowded public park. Everyone can hear you, but it is still a chat with friends.

That line about people whispering because they are afraid to find out who is gone is fantastic. Perhaps it isn't Twitter, but the way journalists have been using it?