First question I would ask is why are you using displacement? What’s the goal beyond this test asset? Displacement is a pain in the ass, hard to edit, and uses a ton of memory. Most productions I’ve worked on actively avoid it, unless there’s absolutely no other way.
He didn't use hard edges in that test, all edges were soft... If you use hard edges, unless you're baking in Maya you WILL get some sort of minuscule seam over the hard edges (and even then!).