I was playing a Secrets of Strixhaven Premier Draft. My opponent had a Quandrix, the Proof and some other creatures as shown in the screenshot of the battlefield.

I cast Impractical Joke targeting one of their creatures. The cast Return the Favor selecting both modes to redirect and copy the spell. Their copied version of Impractical Joke had storm from Prismari, the Inspiration

Prismari, the Inspiration reads "Instant and sorceries you cast have storm". However, their copy created from Return the Favor isn't cast. Gatherer rulings specifically cite "The copy made by the effect of Return the Favor's first mode is created on the stack, so it's not "cast" or "activated.""

The changing of targets also doesn't count as my opponent casting an instant or sorcery so Impractical Joke should not have storm.