Well, terms can be used differently in various disciplines, but my experience with preload is with springs and bearings, where there is an expected force (load) in it's usage and some initial force (preload) used in the installation.

I think in this case we are trying to figure the relationship between bolt torque and clamping force.
I don't have much experience w/ carbon bars (too expensive) so I can only postulate (fancy word for guess).

Whew, fixing stuff is fun; writing about it is a bit more effort!