It’s probably one of those generic pieces of advice that’s too broad. For instance, Ayn Rand interrupting Atlas Shrugged to deliver a 32 page treatise on her philosophy is insufferable in many eyes including my own (I still remember getting 4 pages in to the info dump spiel and starting to search for the end quote), but some readers are there for that.

A lot of times authors pomposity and interruption of a fictional narrative can be distracting and take you out of the story, sometimes not. The real rule is do things well, and serve the audience you want to speak to.