Connecting to a Windows machine with Ansible
There are two places where Ansible looks for group_vars subdirectory:


the playbook directory - the one containing a playbook you run
the inventory directory - the one specified with -i option at run time, or a default one (usually /etc/ansible, or /usr/local/etc/ansible)


In most typical scenario you might place group_vars along with the playbook.yml.

The example you posted uses the second method, so to reference the files you need to add -i to the command:

ansible windows -m ping -i ./windows