I've had many bbls rebored and rifled to a larger cals., and i've also "lapped" several bbls, perhaps that's what he's refering to???
Properly rebored bbls shoot as well as, or "better than", factory bbls., and if for some reason you have a "rough" bbl., lapping it will help smooth it up for better accuracy, and less fouling.
Other than these two, i'm not sure what your friend would be refering to??
Drilling Man