Potential activity is the activity that has been stock in your account ,
It could help you to Rank up without waiting for the update if you reach the potential activity needed to rank up.
It means that the time needed to cover these up is the same and not a way to reach that particular rank but you can by purchasing account that is made a long time ago like hilariousetc said which has stock activity or potential activity.
This is for additional or other interpretation of mine.
by making at least one post every two week you earn 14 potential activity points. Having potential activity can be much quicker to reach higher rank.(actvity score)
As long as you have enough posts to cover it up. Activity count can't be higher but can be equal to post count despite your potential activity and whatso.