In this tutorial Nginx is serving your static files in your code directory and php files is being interpreted by php-fpm.
The key line is fastcgi_pass php:9000; in php-docker.local. This allows to access php-fpm container.
// run image
docker-compose up
Add your host php-docker.local like below
127.0.0.1 php-docker.local
http://php-docker.local:8812/index.php
Or you can test without adding your host file anything with curl like
curl -XGET --header 'Host: php-docker.local' http://localhost:8812/index.php
siege --time=10s -c50 http://localhost:8812/index.php
siege --time=10s -c50 http://localhost:8812/static-file.txt