For me, native means "I can integrate a platform widget in the middle of it". For instance, with Qt, GTK or wxwidgets it's entirely possible to integrate a Win32 / Cocoa / X11 component right in the middle of your app (and it's super important for instance for things such as integrating audio plugins, where the plugin only gives you a HWND or NSView and you have to draw your application Chrome around it, have it follow resizes, etc.)

So then flutter will let you do that, with a little elbow grease.