It's pretty much a standard term at this point in that category of sci-fi. For example, Ben Bova also calls them belters.
I vaguely remember Lois McMaster Bujold writing a book about genetically engineered humans named Quaddies, since they have four arms (in lieu of two arms and two legs) who work in free-fall, but I think that was an interstellar series, and they weren't just in an asteroid belt.