He thought the disabled passenger had left - and closed all passenger car doors from a train door operating panel. He then authorised the train driver to depart.
But at the back of the train, an attendant was operating the mobility hoist to help the passenger and her companion leave.
The train travelled about 1.7m before an attendant pushed the emergency stop button.
The commission said nobody was injured in the incident.
The report found there were "no effective means for the train attendant who was operating the mobility hoist to communicate with the train manager".
The TAIC said KiwiRail had since taken steps to improve operational procedures and improve communication between staff on trains.
These included placing high-visibility reflective tape on the hand rails of the mobility hoist to improve its visibility.
KiwiRail had also installed a light in the luggage van that shined onto the platform when the luggage van doors were open.
TAIC said these improvements meant the commission did not have to issue recommendations to KiwiRail or the wider industry.
Shortly after the incident, an eyewitness told the Kapiti Observer the train conductor apologised to the woman, and she accepted his apology.
"She was still on the ramp ... the train was creeping along. I was screaming out and the train stopped," eyewitness Warren Doughty told the Observer.
KiwiRail said it accepted the TAIC findings.
"As indicated in the report, KiwiRail has taken action to prevent this situation from arising again, including ensuring on-board staff had access to a portable radio and reviewing operating procedures when using the mobility hoist," the company said in a statement.
"The safety of passengers and staff is KiwiRail's number one priority and we take all incidents very seriously and investigate thoroughly."
In February 2013, a woman suffered critical injuries when her chair became stuck on the tracks at Auckland's Morningside Drive.
A jogger and a commuter who risked their lives to push her wheelchair almost out of the train's path saved her.
The 2 year-old woman's chair was caught by the front of the train and she was dragged five metres along the track.