Could be. In New Guinea it was thought by the European colonial powers that the highlands were basically deserted and that all the population was on the coasts. But the highlands turned out to be the most populated. So if people were only discovered there in the 1930’s, who can say what still is to be found there?
Actually, the last people group that I know about was found around 1997 by an linguist/anthropolgist from Australia (I can’t remember his name) and a linguist named Mike Moxness. There have been rumors around our organization that another group is out there, but no one has been able to say definitely yet.
I've read that the population of New Guinea is separated by DNA and elevation. This same scientist speculated that as various groups (in prehistory) migrated there the previous occupants were driven (or retreated) higher into the highlands...and, that this seems to have occurred 2-3 different times.