What's Up With the Title?
A Gremlin By Any Other Name…
We don't know the scientific name of what the mogwai mutate into. Billy gives them the name "gremlins" after hearing Mr. Futterman's story about the mischievous creatures that brought down planes during World War II.
The movie is therefore called Gremlins, because that's a familiar word. Even if you didn't know the WWII legend, you've probably seen them in an old Bugs Bunny cartoon or that Twilight Zone episode with William Shatner.
"Mogwai" is allegedly a Chinese word meaning "evil spirit" or "demon." It's an appropriate name for these creatures, which harbor something very dangerous beneath their cuddly exterior. But if the filmmakers called their movie Mogwai, no one would know that that was.