Neutronium laminate? I'd hate to be the bastard who has to glue that in place.
They used a 3D printer. It's all good
It's an interesting premise to think of the deactivated "antimatter fuel system" in the warp drive pods to have vented out their supply. But what about the antimatter not in the warp drive pods? There is the antimatter fuel in the engineering hull ("That Which Survives") and also possibly the antimatter fuel on Deck 11 in "Errand of Mercy" to consider.
BTW, I do agree that the antimatter fuel is generated as needed instead of giant fuel containers as portrayed in later Trek.