Noob question: Are features like this ooblet’s eyes & white belly likely part of the mesh itself, or a plane projected onto the object?

Here’s an example of what I’m referring to. I’ve been noticing a couple examples of meshes like this in low poly stuff lately, but I don’t know how I would end up doing something similar? I’m specifically referring to the circular parts like the belly and eyes – IDK what the mesh would end up looking like.

When I model little things like this, I’ve been starting from object primitives similar to the shape I want, so my meshes are more grid-like.. If I were to try to color the belly a different color, it’d be a rectangle. I did try projecting a plane for the ears i n this example, but I think I’m doing something wrong. Is my problem that I’m only doing box modeling, and not polygonal modeling?