Hi, indeed the developer guide could be a bit clearer here;
actually in Vuforia 2.0 the new class VirtualButtonResult has been introduced; the VirtualButtonResult contains the flag function "bool isPressed()", so if you are interested in reading the button status (is the button pressed or not), then you should use the VirtualButtonResult, which you can get from the ImageTargetResult (and NOT from the ImageTarget);
on the other hand, if you are interested in knowing the name of the button or other properties (e.g. the Area, the Sensitivity, the Enabled flag, ...) then you need to use the VirtualButton class (and NOT the VirtualButtonResult), whihc you can retrieve from the ImageTarget class;
so, to summarize, VirtualButtonResults are retrieved from ImageTargetResults, while VirtualButtons are retrieved from ImageTargets;
VirtualButtonResults allow retrieveing "isPressed" status;
VirtualButtons allow retrieving all other properties of the button.
You can also check the API reference:
I hope this helps.