Federation Commander

In a recent Federation Commander game, an opponent moved directly behind a moon hex to avoid being hit by a Plasma R. I presumed he was using thinking of the SFB rule (P2.23) where there would be a 50% chance the plasma, at speed 32, would strike the moon. The debate centered on whether a plasma was a unit in this case or not. He actually presumed the plasma would strike the moon based on the FC rule that moons (6A2) were treated as medium sized planets except that ships and other units could pass through. My argument was that the order of precedence rule (2A5) listed seeking weapons as a unit.
We eventually allowed the plasma to strike the moon as the other result would have ended the game during the next impulse when the plasma struck his ship.
My question is simple. Do moons block seeking weapons or not?

Rule (6A2) says that ships and other units can pass through a moon hex without being destroyed. Your opponent's ship was not protected from being hit by the plasma.

The rule quoted pretty much says it all. For the purposes of movement and ship to ship combat, moons are just map decoration and have no effect. To matter, you need to put something on the moon.

Of course, a by-scenario rule could say that a moon is a nav-hazard that may restrict movement and/or block line-of-sight / weapons fire. As always, a by-scenario rule overrides a general rulebook rule.