You are talking about this blog post ->
https://ermanarslan.blogspot.com/2016/06/ebs-ebs-1225-12c-db-installation-on.htmlThis is because the fact -> "In order to prepare for a multi-user installation, you must first create an oracle user account and an applmgr user account. Both should be created with a default shell that is compatible with the Bourne shell.
"Log in as root to run Rapid Install". Then specify the oracle user as the Oracle OS user, and the applmgr user as the Apps OS user."
Extra info:
If you are installing on a machine with only one node to install, or with all nodes sharing the same user, you can run the install as either the root user or the specific user for those nodes.
Reference : Oracle E-Business Suite Installation Guide: Using Rapid Install Release 12.2 (12.2.0) Part Number E22950-31