I had it explained to me once that for something like a u-turn, the accuracy isn't good enough to pickup the distance. Same for when doing a run on foot on a curvy greenway path. It fails to pickup all the little bends accurately. Despite what was said above about accuracy being fine, just look at the track made if you do some repeated cul de sac loops on the same area.
FWIW, the accuracy on runs is off enough using my bike Wahoo Elemnt that on curvy greenway runs where it is FLAT is where I have my slower runs. Somehow, when I run the perfectly straight streets/sidewalks that are instead on the really hilly terrain.......I'm the same pace/mi or faster.
I've gone out to a flat road and trail near my work for a run and tried the same pace as the curvy greenway and I was noticeably faster. Like 20sec/mi.