Well, the non-fictional relevance of the quote is that it represents the views of the author,

Can we even assert as much? I think we just know that Terry Pratchett just thought it good for his book to speak this idea through the narrator. Probably because it lets him (rot13 spoilers for "Guards! Guards!") unir Pneebg xvyy gur ivyynva dhvpxyl va pbyq oybbq, jvgubhg gur ernqrefuvc fhqqrayl srryvat nf vs gurl bhtug gb guvax gung ur'f n cflpubcnguvp zbafgre.