Because of the han unification, you can tell the font renderer which language context you're in and want things to be rendered. MSWord shows you the language in the status bar at the bottom, which is not only used for spell checking. In html, you can add the lang attribute to a tag to tell the browser what language the contained glyphs belong to.
> do you actually believe they would have the fonts with traditional glyphs in them installed and used at all? What for?
Because ever since Vista, these come pre-installed regardless of your locale.
> Do you seriously think CCP officials have a fleet of Macs to check document appearance in case they are leaked and/or scan documents for "enemy" Unicode points?
I don't believe anything in particular, just adding technical context. The documents could also have been leaked through Taiwan or Hong Kong and then mangled there resulting in this.