I've earned most of my posts/stars in the mods forums of the game - pretty much exclusively. I see others with as many posts and I never see them in the mods forum, but they are all over the community threads.
Doesn't matter when they join as much because a person could still only sign up and post a few nonesense words in threads and do that every 6 months. Or they get a new username every year but are as old as daggerfall dirt.
This info is just not telling enough in that regard - and if you don't agree - post 5000 more then we can talk.
I'm not sure where your posts were earned makes much of a difference, mine were in Elder Scrolls Series Discussion before the overhaul if I recall correctly (which is a pretty slow forum)\
Hell, back in 07 you could get to post limit on a "funny news article" thread and CD was one of the busiest areas of the forum, it seems quite dead nowadays.