"Milking" as I understood it was a physical manipulation by the hand(s) during the trigger pull, involving the flexing of more than the trigger finger. This can result in the downward pull.
Mark described the other problem common to dropping shots. That is, the anticipatory flinch that is conditioned via previous shots. Your body, knowing the recoil is coming, will attempt to anticipate the recoil and force the muzzle down. This is not milking per se as the flinch may originate from areas other than the hands, although the hands may be involved. The flinch may be in the hands, wrists, elbows, shoulders, or a combination of parts.