Gigantopithecus appears to be associated with the subfamily Ponginae and thought to be related to Orangs PURELY on the fact that the remains have been found in Asia and are more proximal to areas inhabitited by Orangs. Seems pretty spurious reasoning to me. After all, there are BILLIONS of human who migrated out of Africa and into Asia and NONE are related closely to Orangs, thus rendering "proximity" a weak argument in my opinion.
It has been reasonably argued that Gigantopithecus shared a trait with humans--bipedalism--which differs from EVERY other species of Great Ape and allies it potentially with humans. This is considered a possibility due to the shape of the fossil jaw-bones which have been recovered which are U-shaped like humans rather than V-shaped like apes and would have potentially permitted room for the trachea within the jaw rather than behind it, allowing the skull to sit on top of the spine like modern humans, suggesting the possibility (if not likely-hood) of bipedalism. Seems to me that an undeniable physical trait such as this, differing from ALL other apes and found otherwise only in humans (despite whether Giganto being bipedal is open to debate) should be AT LEAST as compelling for linking the primate with a human relationship as the argument that finding the remains in areas normally populated by Orangutans should associate Gignatopithecus as related to Ponginae. That's akin to making the argument of, "Yeah, it has these strongly human characteristics, certain aspects of the teeth and the U-shaped jaw-bone ONLY found otherwise in humans, but there's a lot of Orangutans around here so let's say it's related to THEM!"
If one accepts the plausibility that North America sightings of Bigfoot represent Gigantopithecus, then CLEARLY it is/was a wandering animal which, like humans, would have managed to cover a LOT of ground during the life-time of the species. If they made it across the Bearing land-bridge into North America, certainly Asia would have also been accessible to them. I wonder what science would say if an artifact containing the same DNA characteristics were to be found in the Canadian wilderness or the Pacific Northwest . . .