Bind and DNS forwarding

[jimbowasthere]

I have an interface that I want clients when heading to an non-internal destination to use an openvpn client connection and use the VPN's servers for DNS. I have that working and I'm not entirely sure why as I have yet to define the external DNS servers.

I have the following setup:

DHCP service for the interface (guest) that sets the DNS server for clients to the same as the gateway: 192.168.15.1
A firewall rule allowing outbound destinations (*) using the specific VPN gateway.
External/Outgoing NAT rules for the subnet to use the VPN interface.

Bind setup to listen on that interface, ACL for the subnet, view that allows recursion, and zone that allows querying by the ACL. I have not setup any forwarders.

I've done queries on client machines (as well as use dnsleaktest.com) while packet capturing on the interface and each time I see DNS queries to the VPN's DNS servers.

Am I missing something?