It's specifically referencing the central idea of the book mentioned in the first sentence of the paragraph.

> Did you get to read the Liu Cixin’s second 3-body-problem novel? - The Dark Forest. Well some of you did …

The author of this post then provides a good summary of the idea in the next few sentences, but remember there is an entire book around this premise (and a first book that sets it up and a third book explores it even more).