They're not all that big. There are a couple things here. First, Kodiak produces big bodied billys. You may not see a lot of B&C billys from Kodiak comparatively, but their bodies are as big as anywhere in the world. The second factor is that he was alive long enough to get big. Kodiak is harsh...
The title had me thinking brown colored mountain goats. Never seen color phase mountain goats before, but after living in Texas for a few years, I've seen a color phase for about every different type of critter.
We found several nice billies when we were there last September. There were a couple that we just couldn't get to, but I ended up shooting an 8 year old 9.5" billy with fantastic hair. I'd put all of the mature billies we saw in the 9" range.