As it says in the window, it's just a sample that shows that these UI elements (radio buttons, combo box, line edit) work.
GDI (Graphics Device Interface) is a Windows application programming interface.

How does this work with the Windows GDI?

GDI was Microsoft's protocol for drawing 2D things like lines, curves, font based text, and other primitives on 2D surfaces. It has been used primarily for Windows 2D screen draw functions approximately forever, although recent Windows versions have somewhat changed in the way that GDI draw calls are handled. It was also prevalent for interfacing printers that didn't have an internal descriptor language like Postscript or PCL.

Apparently the library this is a demonstration of can change it's output target from GDI to another system implementing equivalent functionality.

It says on the screenshot that says that "This dialog has a few types of controls to show that everything can work on a non-GDI display as it does with a GDI based display" so it's saying that you can use Voodoo2 for GDI acceleration?

I have no idea what they were using, whether it was Glide, DirectDraw, or VBE 2.0 under DOS. Based on the evidence, I suspect that it wasn't GDI.

Ignore this thread.

This post of mine was taken completely out-of-context for yet another blind misinformed dumbassed obfuscated goosechase for a silver bullet for an incompetently put together windowed Direct3d ActiveX VisualBasic excuse of a "game". (whose continual persistence has led to a forum ban elsewhere)