This quote from the movie The Shawshank Redemption:
Some birds are not meant to be caged, that's all. Their feathers are too bright, their songs too sweet and wild. So you let them go, or when you open the cage to feed them they somehow fly out past you. And the part of you that knows it was wrong to imprison them in the first place rejoices, but still, the place where you live is that much more drab and empty for their departure.
Can this passage be called a metaphor? If not, what word describes such a comparison?