I don't think that is true. I've gotten decent distance tracking from the watch when in standalone mode on bike rides. It wouldn't have any other way to calculate the distance.Here map can be standalone use. Just can't navigate with it. GPS with S Health is also quite useless as S Health only uses it for location mapping, not actually used for distance calculating.
Biking uses gps. It's why I use biking when kayaking.For walking or running, it is using the pedometer. Not sure about biking.