Earlier quoted context omitted.
The reduced-resolution thing has been a trick for ages, I just refused to use the 4k screen I paid a premium for at half res with horrid (seriously, horrid complete with artifacts and fuzz, I even patched xrandr to disable bi-cubic filtering trying to make it ok and still couldn't stand it) looking text aliasing. I'm impressed you'd call that "pretty much perfect and comparable (if not better) to macOS with a recent…
He hasn't scaled the 4k screen. You can tell because it's eDP or Embedded Display Port . That's something they use on laptops for the internal screen.
It also has the same problems with aliasing, blurriness, and artifacts (the blurriness and bad hinting become more pronounced and the artifacts take a back seat)