It actually did upload stuff silently. Here's what you can do to reproduce:
Have TextEdit enabled in the iCloud System Preferences panel. Open TextEdit, create a new document, type stuff in it. Now press cmd + O to display the iCloud document picker, and you'll see your new document got uploaded to iCloud, without you ever hitting Save or explicitly agreeing to save it on iCloud.
The only way on Mavericks to have 100% local data was to:
a) disable Documents in the Cloud for all apps or a specific app, or:
b) save documents to the local drive immediately after creating them, before typing anything.
I'm surprised this isn't more commonly known, and that everyone seemed totally fine with it. Doesn't seem like intuitive or expected behavior for an average user IMO.
