If I had to take a guess this is related to books that have illegal PDF(s) in th...

TeMPOraL · on Oct 13, 2019

Or legal PDFs. No Starch Press books are regularly featured in Humble Bundles in PDF form, including the book from the Tweet.

jbay808 · on Oct 13, 2019

I got a control theory book from Amazon once which was just the cover. The inside was a veterinary handbook by a different publisher.

I don't think there's a PDF for that controls textbook anywhere, so clearly the counterfeiter just substituted in a different one...