This is a common problem that has to with how VPN software is
designed. It fails open unless you script your firewall to block
outgoing connections when the VPN fails - failing closed.
That's what he is using - VPN-Firewall - Leak Protection (Fail Safe
Mechanism) for (Open)VPN.
This has nothing to do with Whonix. please lookup general linux
VPN-Firewall was created by me. VPN-Firewall is documented in Whonix wiki.
Although not a part of Whonix anonymous operating system.
A small mess up on my side, perhaps.
So from a user's point of view it's not terribly wrong to ask about it here.