Don't think it was necessarily a plot hole, albeit after the fact. Plenty of sci fi authors have taken similar approaches throughout the years. The idea is that in a spiral galaxy the natural tendency would be to stick with the orientation that matched the galactic plane along the right-handed spin (to determine up vs down) and some authors have even extended naval directional signals into space. This is from The Lost Fleet:

"Within a solar system, directional references were always made to the world outside a ship so other ships could understand them. Anything above the plane of the system was up, anything below it down. The direction toward the sun was right, or starboard, (or even 'starward' as some urged), while the direction away from the sun was left, or port."

"The direction toward the sun was right, or starboard, (or even 'starward' as some urged), while the direction away from the sun was left, or port.""

Ehh. Ahh. "Port" and "starboard" should be relative to the bow/stern axis of the ship. Otherwise you'll have a hard time finding the head.

In the future we won't need a head, because we'll have matter teleportation.