Let's step back a bit in the timeline, shall we, and look at the guy Anonymous stole these plans from, Aaron Barr? Want to know why they got tipped off about him? Because he had theorised that Anonymous was not, in fact, the amorphous, headless social phenomenon/semi-sentient meme that we all know it as, but rather a small group of elite hackers with lots and lots of sockpuppets, and set out to prove his theory armed with poor research, monumental hubris, and a desperate desire for acknowledgement at any cost.
Here's what happened as a result.