With his typical unimaginative accuracy, Gulliver is describing, point by point, a very primitive form of human being.
Where did Swift get the notion of a debased humanlike organism? Throughout ancient and medieval times, Europeans remained unaware of any organisms that resembled human beings. The closest were the monkeys (such as the one that plays a rold in Gulliver's trip to Brobdingnag), but these were thought of as, at best, small and amusing caricatures of humanity. There was also the Barbary ape, found in North Africa Ihence "Barbary") and at Gilbraltar, which differed from other monkeys in being tailless.
In the seventeeth century, however, creatures who were "apes" (since they were tailless) but who were much more humanlike (anthropoid) than any monkeys were discovered by Europeans. In 1641 a description was published of an animal brought from Africa and kept in the Netherlands in a menagerie belonging to the prince of Orange. From the description, it seems to have been a chimpanzee. There were also repots of a large humanlike animal in Borneo, one we now call the orangutan. It may well be that Swift, in describing the creatures on this island, was thinking of the vague descriptions of the orangutan.
Oddly enough, Swift was, in a way, well ahead of his time. There was no hint as yet that in the past humanoid beings had existed that were not quite modern humans but were closer in resemblance to us than to any anthropoid ape. Neanderthal man were not discovered for a century and a quarter after the publication of Gulliver's Travels, but the creatures here described by Gulliver might well have been Neanderthals - at least as popular fancy would have had them . "
It seems Jonathan Swift's ability to see into the future held true regarding anthropology as well.