Why is the admin user becoming a member of newly created role in Postgres?

Question

I am quite new to PostgreSQL. We have a database server on Azure Postgres Flexible Server. I log in to that server using the admin credentials, dmsadmin. Then I create a new role using the command, CREATE ROLE dev_user1. Now running the \du, gives me the following output ->

     Role name     |                         Attributes                         |                                                           Member of                                                           
-------------------+------------------------------------------------------------+-------------------------------------------------------------------------------------------------------------------------------
 azure_pg_admin    | Cannot login                                               | {pg_read_all_data,pg_monitor,pg_read_all_settings,pg_read_all_stats,pg_stat_scan_tables,pg_checkpoint,pg_create_subscription}
 azuresu           | Superuser, Create role, Create DB, Replication, Bypass RLS | {}
 dev_user1         |                                                            | {}
 dmsadmin          | Create role, Create DB, Bypass RLS                         | {pg_read_all_settings,pg_read_all_stats,pg_stat_scan_tables,azure_pg_admin,dev_user1}
 replication       | Replication                                                | {pg_use_reserved_connections}

Now if I understand the output correctly, it says that dmsadmin is a member of dev_user1. So I tried to remove that membership using the command REVOKE dev_user1 FROM dmsadmin. Then I got the following warning:

WARNING:  role "dmsadmin" has not been granted membership in role "dev_user1" by role "dmsadmin".

How is that possible?

Thank you in advance.