I guess I don't have a fine tuned sense of what is a spoiler and what is not. If I know I am going to see a movie based on say, an actor I like being in it, I don't want to know anything about the movie ahead of time. Everything is a spoiler. If I start to see a preview of that movie, I'll close my eyes and try not to concentrate on the sound. If I don't know if I want to watch a movie and start reading a review about it to see I should go, I stop reading as soon as I decide I'm going to go and don't finish reading the review. Same sort of situation with books. If the thing you are reading is not meant to be a review to help you decide to go and read/watch, then writing/talking about a work of art without discussing details seems pointless. Why mention the work in the first place. This article is not a book review.
If you consider the standard three-act structure (setup, confrontation, resolution), a spoiler is typically any important plot point from acts 2 or 3. Information about act 1 is much less important, because expectations are still being created at that point, so there isn't much room for twists yet.
For example, the fact that The Tortoise and the Hare involves a race between the two animals isn't a spoiler, because that's part of the setup. The fact that the tortoise wins because the hare is overconfident is. (Or it would be if the tale wasn't thousands of years old and familiar to essentially everybody already.)
In this particular case, the plot point in question is revealed less than 30 pages into the book and can comfortably be considered part of act 1. It's even described on the cover blurb. So, not a spoiler.
You can discuss quite a lot only using details from act 1, and being more vague (or ignoring) acts 2 and 3. In this particular article, everything is from very early in the book, so no spoilers are present.
