I was doing some looking around and found this FAQ on Dixie Gunworks site.

1. How does the barrel rifling affect the performance of the muzzleloader?

The method of rifling the barrel will have a profound impact on the accuracy of the muzzleloader. The rate of twist of the rifling will determine the proper type of projectile. For slow twist barrels (1 turn in 56 to 72 inches) use a patched round ball. For fast twist barrels (1 turn in 16 to 28 inches) use a conical bullet. Medium twist barrels are designed to shoot both patched round balls and conical bullets. Round balls may be used in a muzzleloader with a fast twist with good results. The key is to reduce the powder charge so the ball does not travel through the barrel so fast that it strips the rifling and does not take the twist or rotation. A discussion of other factors in barrel rifling such as different methods (cut, broach, button, etc.), number, width and depth of grooves, while important, is beyond the scope of this discussion.

So therein lies the reason for the fast twist in a ML pistol. Lower velocity due to light charges like I've been saying after a couple responses to my original question. The faster twist is necessary to stabilize the ball at these lower speeds. It has nothing at all to do with barrel length.