No , s/he means a King BaboonHonestly, i'm not familiar with this species. I tried to Google 'KBB,' but all that it brought me was 'Kelley Blue Book' and 'Kitchen and Bath Business.' No Ts there.
I'm being silly (though, i really DID Google it).
I'm assuming you mean the GBB (Greenbottle Blue, or Chromatopelma cyaneopubescens)? I'm learning about this one as i go- my sling is currently at about 3.5", and is still in the gangly teenage phase. My GUESS would be that they thicken up closer to being mature adults?