Author here. The point of the demo is not to show the benefits of indexing. That, you are quite right, is obvious. The point was to show how the database can parallelize application code. Instead of asking the database to perform a query or a transaction, whether synchronously or asynchronously, you pass your data-processing code to the database to schedule and run. The idea is to unite the database and the application, or make the database not just a data-store but also a parallelization framework.
But don't mistake this database to be some sort of monolithic monster running on a huge server and programmed in an obscure language. This database runs the application on the application server, and it uses whatever language the application employs.