Here's why:
Non-fiction:
* Scientific description: It could be used in a scientific text describing the formation of sleet or hail, where the drops of rain freeze in the air.
* Weather report: A weather report might mention "frozen drops of rain" to describe a particular weather event.
Fiction:
* Figurative language: The phrase could be used metaphorically to describe something else, like tears or a cold heart.
* Setting the scene: It could be used to create a specific atmosphere or mood in a story, like a cold and lonely winter scene.
In conclusion: The phrase itself is neutral. The context in which it is used determines whether it is fiction or non-fiction.