Websites don't see your real DNS server. They see your real IP address: this is called the public IP address assigned to you by your ISP.
If you use a VPN, then they see the IP address of your VPN provider, not your public IP address.
AirVPN wants to address the following problem (amongst others) when you use their service by configuring Comodo:
Say you are downloading from a website through the VPN tunnel. And you are using a downloader program that automatically resumes the download when interruptions occur.
Now, for whatever reason, your VPN connection gets interrupted. You are no longer using the VPN tunnel, because it is down.
Then your downloader program will notice that the connection was interrupted, and establish a new connection to resume the download.
But since your VPN tunnel is down, you will connect directly from your machine to the web-server, hence the web-server will register your public IP address.
AirVPN's suggested Comodo configuration is designed to prevent this.
DNS-leaking is another problem they address with the configuration (but it's not a problem you are concerned about).
DNS leaks occur when your machine has a VPN tunnel, but makes DNS requests that don't go through the tunnel (but via your public IP address).
Disclaimer: I only took a superficial look at AirVPN's recommended Comodo configuration. But they make a good impression.
SANS ISC Handler
Microsoft MVP 2011-2016 Consumer Security, Windows Insider MVP 2016-2018
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