It's passive aggressive because the people aren't directly speaking to their neighbors. Kind of like the notes in passiveaggressivenotes.com - those notes are direct, but they avoid direct confrontation.
Then all notes are passive by nature of not being face to face, and they should just be called "aggressive notes." Except many of these aren't aggressive in that they're not deliberately hostile or vengeful, just plain directives that some readers take as personal attacks for some reason.
