Yeah, I get that. Unless you either read about it, or have worked in a corporate environment with calendars that have events pop up on them without your direct intervention, it's not something that would be intuitive.
What's important is that nobody has access to your stuff. They just want you to think they do.
They're used to indicate context because that's how the English language works, my dude.
Sure, in other languages they may not be. But it's universal in many Western languages.