"You are a human, not one of us" (16.370)—that's what Leaf-eater tells Human, and it's supposed to be an insult. Leaf-eater is saying that Human is betraying the piggies by assimilating.
Human is betraying the piggies, in some sense. The piggies were a community, and Human is pushing that community to end. In its place will be a new community—one not just of piggies, but of Humans and buggers as well. Ender prompts Human to realize that "We become one tribe because we say we're one tribe" (17.121), but this is the implication of Human's name from the beginning. Human is ramen, which means that, though he's a different species, he's human. So when Ender writes the Life of Human, he's writing the life of a human, not an alien—or he's making the alien human by writing of it as human.
On the other hand though, it is Ender who writes the Life of Human… after spending only a few weeks with the piggies. His voice ends up defining them; they are human because they are in his words. Human becomes human language, and his name and his story are theirs. So are humans and piggies a new community? Or have the humans simply absorbed the piggies? The novel insists on the first interpretation, but Leaf-eater's accusation lingers, never quite resolved.