or that somebody, upon hearing of the Xindi attack, would've mistaken the name for "Kzinti."
It is worth noting this mistake would have been unlikely as Kzinti is pronounced with a hard k sound: K-zinti.
On the contrary -- people hearing a new word for the first time often mistake it for a similar, but non-identical, word they're already familiar with. Because that's how the brain works -- by association, by trying to map new input onto established patterns in its memory. In a universe where Kzinti existed as an established threat, people hearing "Xindi" for the first time would naturally be prone to think the speaker had said "Kzinti." They might not notice the difference at first, or they might notice it but be unsure if they'd heard correctly, or they might wonder if the speaker had misspoken.
Heck, I once had a high-school science teacher who said "Aristophanes" (the playwright) when he meant "Eratosthenes" (the scientist). And an honors English teacher who pronounced "synecdoche" as "synectady." These were people who really should know better, and they still got the pronunciations confused, not just once, but as a matter of habit. It happens all the time.