There isn’t a native word AFAICT, it’s a loan word. But taking real things and making a slight change to be something new is pretty common for games. For example, final fantasy uses “Gil,” which is abbreviated “G” and probably comes from “gold” (gil - > gold is a pretty easy jump), though the in-game explanation is different (name of in-game ruling family).

I think it’s highly likely Miyamoto didn’t know about the Indian rupee.