Shaded preview mode in GH also calls DrawViewportWires method

I was wondering if anyone knows why this is happening. From Grasshopper’s preview modes - no preview, wireframe, shaded- I have the shaded mode selected.
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I have a IGH_Goo implementation with separate logic for drawing wires and meshes in the DrawViewportWires and DrawViewportMeshes methods respectively.

What I am observing is that, when wireframe mode is selected, only DrawViewportWires is called, but when shaded mode is selected, both DrawViewportWires and DrawViewportMeshes are called. Is that by design or am I misunderstanding something?

Bonus question: Is there a way to get the currently selected preview mode via the API?