China was involved in meetings before the movement was formally declared, both because they were seen as important to others organizing the beginnings of the movement (they were seen as a kind of pivot-state by everyone—their strategic and negotiating strength was tied up with a kind of potential energy, should they throw their weight behind any other player) and (probably) because China was angling to steer the movement as their own bloc, but they weren't part of the actual founding conference in the quoted paragraph, and only obtained observer status in the group in '92.