I think he is a bit quick to dismiss some of the alternatives, such as Xamarin. He says, "It can only output to intermediate Xamarin libraries, not native ones." I'm not quite sure what he means by that and why that's a problem. Xamarin outputs to .net assemblies, and in the case of iOS will further be compiled to native code. It is completely possible to call native libraries on those platforms; both Java & C/C++ on Android and Objective-C and C/C++ on iOS.

Xamarin like any library except HTML5/javascript, cannot produce cross-platform UI code. But lowerlevel -- database and networking code -- can be reused. In fact, those libraries could be coded directly on Windows, OSX or Linux, where it would be easier to develop and test.