Yeah, it's made clear that the tempered sylphs are also high as airships on milkroot (something the 'good' sylphs of Little Solace hate, regarding it as a curse on their society) - kupo nuts however just seem to be a tasty food that the moogles like, it's their traditional signature food throughout the FF series after all, like chocobos and gysahl greens.

At least this time around kupo nuts are properly translated, in FFXIV 1.0 they were called 'pearl clover fruit' for some reason. But I digress.