Ok I think I know what is going on. I think the admins are playing around with default titles. So if you dont have anything custom in there it defaults based on what stage your account is in. So for example you have over 10 thousand posts so it changed. Similar to how a brand new member will say new member or active member ect...
I THINK that's what's going on here.
There's always been text there; it's known as the "title" in the software. By default, the title changes as each member's post count goes up, and what it says at each interval of change is set by the admins in a universal fashion for everyone.
I'm guessing the last interval was at 10k posts, which you've been past for some time now.
Members have the option to change their own custom titles, which is why you see some people with non-defaults. But if the field is blank, then the default is used.