Well, one problem is that you don't just have n-gons there, you have n-gons with interior holes in them for those planar faces.

I don't believe that the OBJ format has any way to express holes in polygons.

Which software is he using there, is that Hexagon? What happens if you export that cleaned up shape from Hexagon out to an OBJ file and then read it back in again, does it maintain that same structure or has it become triangulated?

- Michael