The video was posted because it proved that the GPS is accurate enough to get a speed.
The GPS offcourse is accurate but I told you in my above post that its accurate to the extent of 1meter that is also not concretely defined and there maybe a bit of diversion in accuracy from vendor to vendor, I think the video you posted shows GPS and oled display etc mounted in a car. but you want it to do for your RC car and an RC car covers less distance.
Just use a optical rotary encoder to read the pulses per rotation and calculate the speed, goto polulu's website.