It is using the platform's API directly and renders native components. The XML is just an abstraction layer on top of that and not a web wrapper like you're implying. It's not using any WebView.
It's easy, instead.
It may render native components, but those components are still controlled by the non-native runtime, thus extra baggage.
It would definitely be using native UI components, which a normal web browser won't give you via the rendering engine.
But that's as native as it gets. The control logic for how those components operate outside of how they're internally built is likely done w/ React / JavaScript, instead of native.