The Tvheadend interface for the HDHomeRun tuners assigns a type upon first seeing the device based open what the device reports its name as. If you are using an older version of libhdhomerun (or if your Tvheadend was compiled statically against the older version) it may not know what type it is: I believe DVB-C is the default it uses.
In the Tvheadend interface, select the HDHR device (the parent of the "Tuner #0" and "Tuner #1" entries) and change its network type manually to DVB-T. It will save the override so the next time you restart Tvheadend it will continue to use your DVB-T setting.