In the past member titles like "established member" were based exclusively on the number of posts you made. If you wanted to perceive a members seniority with information you'd have probably looked at their 'title' and the number of posts they'd made.
These days, a members perceived value on the forum may not come about from simply the number of times they post, but also the length of time they have been a member, the amount of reactions (likes, informatives) they have received on their posts from other members and perhaps future values too. All of these values, including posts, earn points at certain milestones.
In the future, while you may still look at a members 'title' the preference would be to only see a point value, not a post count. You can then click on the point count (hover over an avatar with your mouse and click on the point count to launch an overlay) to see where they have earned their points from.
