Procedural "Faceted" Terrain

I was wondering if anyone would be interested in assisting me. I was curious if anyone would be able to supply me with the information I seek. I was curious, how does one produce “faceted terrain?” I want to make a low poly game, with faceted terrain, like this

I’ve used perlin noise before, but I was curious as to how I would implement this. Is this a plane? Thank you very much!

Check this video, it explains how to add flat shading to perlin noise procedural terrain: