What's native about it? It seems like custom GPU rendered thingy with nothing "native".
Linux GUI frameworks are hot potato, I tried to write "native-feeling" app with taskbar icon lately on Linux (Cinnamon), intuition says GTK3, Internet says GTK4. Cinnamon says write it in JS and plug it in as an applet. Qt seems like the most complete GUI framework, but I don't like KDE (and Qt on mostly GTK based env looks weird). Windows is the same, Microsoft has like 10 different UI frameworks from different epochs. MacOS seems to be the only one with some common UI framework.
Native in the sense that it renders using the GPU directly (or rather via WebGPU) instead of relying on a webview.
On Linux you're right to say it's basically choosing between gtk and qt.
If it's compiled code, it's native.
Why would you need KDE to use Qt?
And IIRC Qt has a GTK theme nowadays that makes it look not terrible (high praise, I know).
Seems to be "native" as in "not a web-browser/view".