"His only excuse is that he is merciless to himself too. He lies but he does not lie to himself."
Coetzee's Boyhood is a memoir, but as the above shows, it both does and does not provide what a memoir is supposed to offer.
It does not provide what a memoir is supposed to offer because, instead of being written in the first person and the past tense, it is written in the third person and the present tense. Still, try the above in the "normal" form of a memoir: "My only excuse was that I was merciless to myself too. I lied but I did not lie to myself." — The distance created by the third person allows JMC to say things that would sound awful in the first person, while I think the present tense (which I dislike in narratives, usually) is supposed to provide an immediacy that the third person undermines.
At the same time, Boyhood does provide what a memoir (at least a novelist's memoir) is supposed to offer: a "portrait of the artist as a young man" that points toward the artist's own later works.
I have often heard JMC been admired for his obvious writing talent but simultaneously criticized for being cold, cruel, heartless, distanced — this is often connected to a complaint that his main characters are completely unsympathetic. The above passage from Boyhood reads like a response to such a complaint: "I may be merciless, but I am most merciless to myself, so I have earned it." Or rather, "he may be merciless ..." :-)