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If you don't understand something, ask or have a look at the tens of threads in Meta which you can search for.
For the umpteenth time, activity works as is written in the 'code' :
time = number of two-week periods in which you've posted since your registration
activity = min(time * 14, posts)
Activity is updated every hour.
There is an 'activity period' every two weeks, starting tuesday. If you manage to make a post during that activity period you 'claim' the activity. But as activity is never higher than posts , to fully claim all of the activity you have to post 13 more times(if you have made a post in the activity period, you can claim the remaining 13 activity any time by posting 13 posts). Once one activity period finishes, another ones starts letting you claim another 14 activity points.
see this user profile he post over 2000 times but his activity is 364 because he was active for one year.his Date of Registered is November 03, 2013 and last activity is October 24, 2014.In 2016 still his activity is 364 because after that he never login his account.
https://bitcointalk.org/index.php?action=profile;u=156892The user you linked has an activity count of 364 because he has posted in 26 activity periods.
You could also go back in this thread and see others post the correct explanations

but nope you have to mislead others