No Isolation between Main website and Subdomains?

I created a subdomain today and it's located at
/var/www/xxxxx/subdomain.example.com
The main website is located at /var/www/xxxxx/public_html

Both the main domain and subdomain site have the same Unix user and group. So they are not isolated, right?
Same PHP container as well.

Thanks

No, its not isolated because you created it inside the same website account