In tinydns, "Enable recursive DNS responder" means to enable dnscache, its partner in crime that handles recursive queries.
They can't both bind to the same IP, so you tell tinydns to bind to some interface/IPs, and you have dnscache bind to others.
I much prefer the pfSense DNS forwarder (dnsmasq) because it actually works. It's not dnscache's fault it's mostly broken, but few have been interested in fixing that part of the package to get all of the files/syntax correct. And now that it's not really necessary, it may be better to just remove that option.