"Native app" on Mac usually refers to an app following the Apple's HIG (Human Interface Guidelines), using OS native components and having integrations with native services (such as Keychain or iCloud).
The reference browser (produced by the OS manufacturer) on macOS is Safari. It sets a standard for what a 'native' browser following HIG should look and feel like.
You could also say that the reference web rendering engine on macOS is WebKit, which is not only made by Apple but is also the fastest, most resource efficient (probably what OP refers to) and comes with many native system integrations built-in.
In all these regards, Orion is indeed a native app on Mac and many other browsers are not.
The reference browser (produced by the OS manufacturer) on macOS is Safari. It sets a standard for what a 'native' browser following HIG should look and feel like.
You could also say that the reference web rendering engine on macOS is WebKit, which is not only made by Apple but is also the fastest, most resource efficient (probably what OP refers to) and comes with many native system integrations built-in.
In all these regards, Orion is indeed a native app on Mac and many other browsers are not.