20km is less than what he has left of charge. If the detour is earlier in the drive. He could have gone to a supercharger. If he gets stuck in a jam for hours, it makes no difference. The car hardly uses any power when standing still, it will heat the cabin but other than that it uses no power. I've tried this myself, I once got stuck in double digit cold for around an hour in a model 3 outside Hamar. It made no difference to my range.