I'm confused at the others confusion. It has nothing to do with dull; it's simply using a gerund. This form is pretty common. Some examples: Kansas City barbeque is good eating. The climb up this trail is tough going. The latest Amazon series is very boring: it's dull viewing. Guns Germs and Steel is interesting reading.

The sentence does sound strange to me as well. I would say something like "the novel was very dull," or "reading the novel was dull."

All I can gather is that the novel was boring 😄😩

I agree with Micheal that that sentence sounds weird. I also searched in the Oxford collocation dictionary and there is no sign of "dull" used ad adjective before reading. These are the most common adjectives that collocate well with reading: compelling, compulsive, fascinating, good, interesting | depressing, disturbing | heavy, serious | light | compulsory, essential, required | recommended, suggested | background, introductory | further | bedtime, holiday. This is to confirm the less common(to say the least) use of "dull" as adjective in front of "reading".