It might be possible that
Rollin.io was a Legendary member but due to a huge number of deleted posts his activity went down as well. If I deleted more than half of my posts, I would get demoted to a Full Member but my merit would remain the same. A few months ago, moderators deleted many useless threads. He might have posted in a lot of them.
I believe the merit score of any user can only be dated back to the last 120 days and after that it can no longer be traced.
BPIP allows us to track a full merit history.
It's quite simple, some hero member got extra merit when the system was introduced, you can see in here theymos mentioning it:
This post explains why everyone got a different amount of sMerit. It's not the same.