Dunno if i understand this part correctly but users.yml and wordpress_sites use the same “admin_user” but they do 2 different things. The one in users is the username for ssh, but in wordpress_sites for development environment it is used for the wp login.
So it may get a bit confusing even in the Docs. Would it be an improvement if admin_user in users.yml would be rather something like root_user or ssh_user?