I'm a programmer since >30 years ago, have studied mathematics, can speak >5 languages, have programmed in more dead technologies than an average programmer knows current ones, and I don't know what those words mean.

You would have to actually be in the KDE user community to understand this terminology. KDE Neon is the distro that KDE created. What they are trying to say that its based on their flagship Linux distro. I think they might have written that in the most new user unfriendly way they could.

Root file system (rootfs) that's based on dev-unstable branch of KDE Neon. This doc is obviously not aimed at non-techs, but for Linux-savy people the first sentence should fully explain the heading.

I think you mean KDE-savy - I've been using Linux for over 20 years and had no idea what this heading meant.

"reference rootfs" makes it obvious what it is to Linux-savy people, so you don't need to know what Neon is to assume that it's some kind of a distro.

I would say that is very debatable, but it is possible that I am not Linux-savy enough.