Author here. The link is a 6 years old presentation. The demo app has since been rewritten.
The old demo app focused on the downsides of classic multi-page apps (MPAs), i.e. the reason the world moved to SPAs all these years ago. In an MPA clicking a link loses all transient state, like focus, scroll positions and unsaved form state. This can all be solved with updating fragments instead of full pages, while still keeping rendering logic on the server.
