According to the above cited article, there is a 45 cm. passage in the DC-10 [nose] landing gear that leads directly to the cockpit [more likely nose bay].
If so, there would have to be a door through the pressure vessel.
The stowaway jumped out as the groundcrew was about to plug in the GPU and was in good enough shape to take off running.
Could have been an inside job in more than one way
