Devices calculate your stride length based on your height and naturally a person with a wider stride is going to cover more distance in the same amount of steps. Each device calculates the stride length slightly differently.
So, how does this affect your challenge?
Well, depends on the challenge. Most challenges are counted in steps, so the stride length isn't really a factor.
However, Journey Challenges are tracked by distance in miles. In a Journey you may see some players in the lead with a small amount of steps because they have a wider stride.