If they're unlike things - it would be a metaphor.
When it comes to similes - you use words such as like or as when describing things. and since it emphasizes "unlike" things - metaphor would be the way to go.
It's quite hard sometimes when it comes for deciphering the two if you're familiar with the rule - so just remember: Simile: like or as.
Metaphor: extreme exaggeration, or a comparison without using like or as.
I hope all is well, and you pass! (: Good luck, rockstar! (:
