You need a name to get it into Australia. The Brazilians already mislabeled it as humilis, so that will do for the seed import. I guess the name just stuck post import.
It was the Bolivians that made the mistake of calling it G. humilis.
The Brazilians made the mistake of calling it Rheedia laterifolia, you can see that label in Lorenzi's book. Problem is that there is no such name, never existed. It was a misspelling, should have been spelled correctly as Rheedia lateriflora.
Problem is Rheedia lateriflora, now that Rheedias have been lumped into Garcinia, was renamed to Garcinia humilis. Error comes full circle. So i think you can see how Bolivians made that mistake.
Believe it or not lots of species still remain unnamed by taxonomists, especially in Garcina genus, which hasn't been revised in 150 years!
Garcinia sp. may not be very descriptive, but it's a whole lot better than giving a name that really refers to a whole totally different plant, as is the case with G. humilis.
Really even calling this plant achachairu is quite confusing, because almost all the garcinia species in Bolivia are called achachairu. At one point i suggested calling it achachairu of Santa Cruz, but that never stuck.
Anyway, a rose by any other name is still a rose. Despite the naming difficulty this is still a very good fruit!