Granted, I'm not a PS/InDesign/etc pro, but I feel the same way: just not sure what I'm looking at here.

Can someone please explain what this is?

See, I am, and I'm still not getting what the story is here especially in relation to "pixel perfect." The guides demonstrate an attention to detail in getting a good corner, but that's nothing to do with the final pixel rendering as such.. really just good Illustrator path building.