I assume that the top right sphere is using triangles, but is there a reason why it looks more made of quadrilaterals instead? Is that just how it works out?
I think the reason has to do with the triangulation of the sphere. Perhaps it just happens to be that sphere is triangulated in a way such that every pair of adjacent triangles that forms a quadrilateral is assigned the same shade.
I would say "every pair of adjacent triangles that forms a quadrilateral is" facing in the same direction as given in the mesh (.dae file). This results them having the same surface normal and thus same shading value.
Funny, you can clearly see the hexagonal pattern of lighting in the middle "sphere" elucidating the mystery of if the quadrilaterals are triangles. (Look closely, you can see the edges that were previously invisible)