Compare how they talk about the Qu vs the Gravitals.
With the Gravital's genocidal invasion, they're surprisingly fair. They point out that the Gravitals have their own reasons for doing their deeds rather then simply being evil, discuss that they're individuals and that most of them weren't involved in the genocide and seem slightly pitying about their subsequent discrimination. It doesn't gloss over their atrocities, but it does treat them with some degree of understanding. At the very least, it's clinical.
With the Qu, however, that sympathy vanishes. They explicitly refer to them as monsters- while the Gravital are "not evil from their perspective", the Qu have "blind, unquestioning dogma". It describes their atrocities not in the clinical way that it does the Gravital's, but in a way that clearly frames them as vicious monsters.
Now, this might be explained as the Narrator being human and thus taking the human viewpoint, but unless they're radically lying, that's impossible. But what else might explain it is guilt.
If the Narrator is a Qu, or at least one of their descendants, then they might well look on what their ancestors did with horror, seeing it far worse then the actions of an unrelated species- actions which were, indirectly, the result of their own crimes.
The Gravitals acts were atrocities, sure, but alien ones from a long dead species. The Qu's acts are the sins of their own ancestors, and they make sure to hammer home how horrific they are, to ensure that they never happen again.
The ending of the story claims that Humanity "re-encountered and subdued the Qu". It does not, however, say what the nature of the Qu's defeat was— whether they were completely wiped out or, like the Machines, assimilated into intergalactic civilization. The Machines, after their defeat, were heavily altered by the Asteromorphs, both physically and mentally, so that they would never again pose a threat to humanity. Presumably something similar happened to the Qu, and the Narrator is descended from them.
The Qu were a ludicrously advanced civilization of bio-engineers who never settled permanently on planets and believed they had a mandate to forcibly reshape sapient life as they saw fit. By the end of the book, the Asteromorphs are... a ludicrously advanced civilization of bio-engineers who never settle permanently on planets and believe they have a mandate to forcibly reshape other human species as they see fit. They even look
◊ similar
◊. Perhaps millions of years before they invaded humanity, the ancestors of the nomadic Qu fought their own wars against aliens and other Qu species, which forced them to become Space Nomads and convinced them they had a responsibility to control other lifeforms to prevent the emergence of Gravital-like genocidal civilizations.
Relating to the WMG above, the Qu and Asteromorphs became very similar to each other in terms of intelligence, body plan, and behavior. Maybe at some point during the conflict, a few Qu and Asteromorphs would realized that from reading each other's history books they steal, that they're not so different and ended the war in peace, allying themselves to make sure that no genocidal civilization would emerge again.
