Quite a few techniques come together... simple and tortuous are antonyms (have opposite meanings), so the second sentence has two juxtaposed similes.
Also the sentence structure is important as the second one is a truncated sentence - meaning that things important to correct grammar are left out but the important stuff in terms of meaning is still there in this sentence. If it was a proper sentence it would say 'It is as simple as a glass of chocolate ....' As another person said, the other sentences are one word sentences, gives a sense of immediacy and a short impression.
Interesting extract though, might search from other techniques in it