The author is not confused about non-native resolutions; they pointedly mentioned that regardless of settings, they could not get lower screen resolutions to fill the entire panel:

  Regardless of panel scaling options, the UP3214Q would not
  fill the screen at lower resolutions.

Since they were talking about the nVidia card in the context, I assume they're talking about the nVidia control panel settings for this. But it's possible they were referring to some options the display offered.