In the 1980s, Americans were especially wary of China, one of the more powerful communist countries during the Cold War. This anxiety toward China shows in films like Indiana Jones and the Temple of Doom or Big Trouble in Little China. If your only view of China and Chinese people came from '80s movies, you would think all Chinese people were strange, magical, and maybe a little evil.
Or, you'd think (rightly) that 1980s movies were strange, paranoid, and maybe a little xenophobic.
Grandfather isn't evil, but he is strange and maybe magical. How else did he come into possession of a one-of-a-kind mogwai? Grandfather wastes no time in warning Rand that the mogwai can be dangerous, and he doesn't want to part with it. Here's what he tells Rand.
GRANDFATHER: I'm sorry. Mogwai not for sale. […] With Mogwai comes much responsibility. I cannot sell him at any price.
Grandfather's a big Spider-Man fan, obviously.
You'll note it's the grandson who steals Gizmo and sells it to Rand. Grandfather reclaims Gizmo at the end, after the evil gremlin invasion has been stopped. A little too late, gramps.
When he recovers Gizmo, Grandfather is upset that the little mogwai has been taught to eat junk food and watch TV. Grandfather is old, and a traditionalist. He doesn't want Gizmo being Americanized. And what's more American than potato chips and bad TV?