This is called “GPS drift” where the satellites get a little scrambled about your exact position, so you either move a little or jump around a bit. Given that Pokémon GO tracks egg hatching and buddy distance through GPS, not a pedometer, these small GPS drift shifts can actually add up over time and give players distance even when they’re standing still. Shouldn’t GPS drift not count? • The entire endgame of Pokémon GO now is essentially egg hatching and buddy walking to fill out your Pokédex. The process is already painfully long to get all the Pokémon you’re after, and every little bonus, like from GPS drift, helps.

Source: Forbes January 17, 2017 16:11 UTC