I only have half an answer: Markov chains. It's probably going through text and using Markov chains to create "similar" text. Then question then becomes what t

I only have half an answer: Markov chains. It's probably going through text and using Markov chains to create "similar" text. Then question then becomes what text to go through, how long the Markov chains are, how you vary them, etc. Not long ago I took a workshop on algorithmic music where the lead professor had published a book of haiku. The vast majority of the haiku were algorithmically generated via Markov chains, while a very slim minority were actual haiku from 17th century Japan (iirc) translated into English. Guessing which haiku were "real" and which algorithmic was very hard to do.