Unfortunately, they only seem to implement read use cases in that example. I'd love to see how they implement writes with this architecture, as that is where things are getting more complex.
Either they'd make the entity model e.g. a managed (JPA) entity model, thus violating the hexagonal architecture approach, or they'd have a separate model for persistence, but then they'd have to synchronize all changes between the actual model and the persistence model, which depending on the size of the model may be come unwieldy, as they'd loose all the comfort of dirty checking in a managed object graph.
Either they'd make the entity model e.g. a managed (JPA) entity model, thus violating the hexagonal architecture approach, or they'd have a separate model for persistence, but then they'd have to synchronize all changes between the actual model and the persistence model, which depending on the size of the model may be come unwieldy, as they'd loose all the comfort of dirty checking in a managed object graph.