In the source poems, the moon, sun, crescent, garment and buttons are combined into an imagery system that departs from their ordinary external relations. The words retain recognizable meanings while participating in an imaginative scene.
Calling the moon a cup or a beloved the moon is not an external identity claim. The language highlights a feature or affect, allowing imaginative premises to generate something like a conclusion.
Main rule: before interpreting an apparent poetic inference, identify its literal assertions, figurative relations and intended emotional effect.