Theymos was active in the forum back in the day and from the oldest too I think. It's not like he joined the forum and made an admin. Forum was created in 2009 while theymos become an admin in 2012. That doesn’t ensure anything like you are expecting.
Well, there is a part that Theymos joined the forum and few years later become an admin. It is the same in my experience before where the forum I joined is running as it is then later on the forum admin needed a moderator/staff. I applied and got the position as moderator to help manage the forum and delete posts. It was a forum for cryptocurrency but as of now, it seems it can be accessed but cannot log in.