That confirms what I suspected.
As a related rant: the terminology used in the API document is very inconsistent. 3D Annotations refer to the 3D scene, 3D markup refers to GD&T like content in the 3D scene whereas these terms refer to commenting tools in the Acrobat/Reader interface.
You can do pretty much anything you want via the SDK (using plugins or IAC), as even when there's no direct access to the UI tools, you can write low-level data into the PDF (creating a 3D annotation is fully documented in the ISO PDF extension). However, questions about using the SDK should be posted to the dedicated forum, where the engineers can provide detailed help.