I assume you mean during the 'drifting' part where you are not pedalling?
Well, it can be due to a few things, or a combination there-of.
Your brake pads might be slightly too tight and skimming your tires, thus slowing them down significantly all of the time.
Your wheels might need to be oiled up around the axle.
Or your bike could just be of a cheaper, heavier material, that isnt designed to 'glide' for long periods of time, and your friend might have a better bike made of more light-weight aerodynamic material.