They just don't have any concept of real exercise, so they have to guess.  I walked for around 200 minutes at an average pace of 5 km per hour  Who the fuck measures a 17km walk in minutes? Any person I know that actually walked 17km will say "I walked 17km," not "I walked 10,000 steps at an average pace of 900 milliseconds per step for 12,000 seconds and an average stride of 0.4 meters."