What does the term “geometry” refer to in graphics programming?

Can someone explain me how this simple OpenGL example from LearnOpenGL.com can use 500mb of RAM? The shader only needs the diffuse texture and with the model its only 12mb. I am talking about this chapter: https://learnopengl.com/Model-Loading/Model, here is the code:
https://learnopengl.com/code_viewer_gh.php?code=src/3.model_loading/1.model_loading/model_loading.cpp

My frustum culling is detecting an object as culled even though not the entire object’s bounding sphere is out of the frustum yet. It’s like it believes the bounding sphere’s radius is smaller than it is, although I’m confident that’s not the case.