When an author interrupts the story

I'm currently reading 'A Long Silence' by Nicolas Freeling.  It's been a curious book from the outset, but it has taken a very odd turn from about halfway through.  Freeling interrupts the story immediately after he kills off his detective to provide a personal account of the real life detective on which Piet Van der Valk was based and his relationship with him and his wife.  It's a strange interlude, especially as a lot of it is not that complementary and quite misogynist.  And it totally disrupts the narrative flow of the novel.  Moreover, Freeling continues to insert himself in the rest of the text, as if he's recounting the story on behalf of the detective's wife, whilst at the same time making judgements about her.  It's either a clever piece of postmodern fiction or a very odd series of interventions.  It's the kind of thing that is usually reserved for an explanatory endnote.  At the moment, I'm not at all convinced it's a clever piece of postmodern fiction, but maybe I'll change my mind by the time I reach the end.