Since it was a wizard that used the term midbie/highbie, you could deduce that
he didn't have any "game knowledge skillz" in mind when he used the term.
Furthermore, since it's and area (calling one room an area might be stretching
it a bit?) in question you might deduce that codewise it's hard to create a
personal scale of highbie/midbie. Would you compare the time spent in the mud?
Then Obanez is a highbie. Or rebirths? Then Delveling would be a highbie.
So, if you exclude all the little things that REALLY makes the difference
between highbie and midbie, just one thing remains.
Level.
Since we wizards are grey-bearded old farts with no common sense, we use this
simple formula:
(Maxlevel - Minlevel) / 2 = MID. The upper extreme would be highbies and the
lower extreme newbies.
Good enough for you?