Probably by "default" he meant D/R set to 100% and Expo to 0%, which would give you direct 1-to-1 response, the fastest control you can get. However, on the DF the first three channels are set to "Reverse". "Normal" and "Reverse" are arbitrary - on an airplane for instance, the control horn might be on the top of the elevator or the bottom, so there's an easy way on the transmitter to select the correct movement. If "Factory Default" sets all the channels to "Normal", your roll and pitch would work backwards, and your throttle would be at full bore with the stick full down [X(].

Also note that for CH 4 (Yaw) the End Point Adjustment is set to 140%. This no doubt has something to do with the specific circuit design, but I would guess that if you set it to 100% like the other channels, you would not get the full response from that channel. One thing interesting about the DF is that it is a "slow yawer" - just the opposite of what makes most RC helis so hard to fly.