Most toolkits, including WebUI 3.0, render widgets on their own, so you can't distinguish just on that. I'd say anything written in an interpreted language is not native, and Javascript falls into that category. Dart at least is possible to compile ahead of time, and so is C#.

WebViews aren't written or rendered with interpreted languages either. It is also usually not Javascript that makes browser based apps so heavy. It is almost always the whole browser stack that is making them large and memory hungry, which is mostly written in C++.

You can also hook a WebView up directly to a low-level language and skip Javascript entirely, so does that mean Rust + WebView = Native?