Then why send a cryptic warning to Kes? Why threaten to destroy Voyager? The Undine must have known they weren't Borg.
Why did they send a warning? The Undine were lost, confused, and under attack by species they didn't know existed, from a universe they didn't know existed.
If we as humanity came under attack from interdimensional cyborgs intent on removing our free will, tell me, in all your experience with humanity, particularly America, would we not respond with as many nukes as possible?