There seems to be some confusion or mislabeling going on, as I've seen the common name "Bacupari" put on a variety of different fruits. This may be similar to how in the southern Americas "sapote" is a general classification of soft and edible fruit, however we know call many different fruits sapotes. I have seen bacupari labeled on both G. brasiliensis and gardneriana, however the way that I tell the differentiate between the two are based on the fruits. G. brasiliensis, which is sometimes also referred to as Rheedia edulis, has a conical expression on the ends where the stigma can even be pronounced to a "nipple", the flesh is semi translucent. G. gardneriana fruit are more spherical and have a whiter, more opaque flesh compared to "lemon drop" as well as being larger in size.
How old was your gardneriana before fruiting? I am currently on the lookout for a source, I've been checking Oscar's fruitlovers page every day lol
