There are 2 ways to manage access to apps in IBM Cloud. That tutorial demonstrates how to replicate an application from the Identity and Access Management (IAM) model to the Cloud Foundry management model. You wouldn't normally need to create an alias unless you wanted to do this.
Aliases are connections that hold references to remote resources across the platform. They're useful for application management facilitating interoperability and re-use. In this case, the alias is a connection between the IAM-managed service and the Cloud Foundry service and the connection reference will be visible in your CF org or space. If you wanted, you could create connections between your IAM service in multiple CF region, orgs, or spaces.
More information on aliases and managing connections here:
https://cloud.ibm.com/docs/cloud-foundry-public?topic=cloud-foundry-public-connect_app