When you visit someone else's domain and see your site instead, this is most likely not intentional mirroring of your site.
The most common cause of your site showing when you visit someone else's domain name is that they used to have your server's IP address and their domain's DNS is still pointing to your server's IP address.
This can occur when the default app has been enabled on your server.
To prevent your site from appearing on someone else's domain when they forget to change their DNS, simply disable the default app and enable domain blocking.
Go to your app's Settings tab in ServerPilot and click the switch for "Deny requests for unknown domains" so it is enabled (green).
With this setting enabled, requests for any unknown domains will be rejected by your server.