I have a domain and I want wordpress to run at wordpress.domain.com and ghost to run at domain.com. I have installed both wordpress and ghost (on 2368 as suggested in default).
I have a zone file of

$ORIGIN domain.com.
$TTL 1800
domain.com. IN SOA ns1.digitalocean.com. hostmaster.domain.com. 1462332598 10800 3600 604800 1800
domain.com. 1800 IN NS ns1.digitalocean.com.
domain.com. 1800 IN NS ns2.digitalocean.com.
domain.com. 1800 IN NS ns3.digitalocean.com.
domain.com. 1800 IN A 188.166.244.167
domain.com. 1800 IN AAAA 2400:6180:0:d0::552:1
www.domain.com. 1800 IN CNAME domain.com.
wordpress.domain.com. 1800 IN CNAME wordpress.domain.com.```

and the NGINX config file server blocks as:

server {
        listen 80;
        root /var/www/wordpress;
        index index.php index.html index.htm;

        server_name http://wordpress.domain.com;

        location /  {
                try_files $uri $uri/ /index.php?q=$uri&$args;
        }

        error_page 404 /404.html;
        error_page 500 502 503 504 /50x.html;

        location = /50x.html {
                root /usr/share/nginx/html;
        }

        location ~ \.php$ {
                try_files $uri $uri/ =404;
                fastcgi_split_path_info ^(.+\.php)(/.+)$;
                fastcgi_pass unix:/var/run/php5-fpm.sock;
                fastcgi_index index.php;
                fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
                include fastcgi_params;
        }
}

server {
        listen 80 default_server;
        listen [::]:80 default_server ipv6only=on;
        server_name http://domain.com;

        location / {
                proxy_set_header X-Real-IP $remote_addr;
                proxy_set_header Host      $http_host;
                proxy_pass       http://127.0.0.1:2368;
        }
}

Now the problem being both wordpress.domain.com and domain.com both resolve to the ghost installation.
Why is this happening and how can I rectify it?

Thanks