Comment by achipa

This is a more full-stack approach - Qt and Xamarin are geared more towards creating standalone apps. What you get here is the reactive back-end (plus web-site for free). This setup can be used for both data and UI - you could for example publish a new UI (not just content), and all native apps would automatically be updated on the fly. If you take a look at the video - if you do this with Xamarin (or Qt) you would need to manually connect to a database or poll a RESTful service to see current data.