His goal was to answer the interesting question: "how many hashes could I manually generate per day," not to generate hashes in the most efficient manner possible.
Also, the author did not spend two days. he spent 17 minutes and then did the math to calculate the block hash rate.
> Doing one round of SHA-256 by hand took me 16 minutes, 45 seconds. At this rate, hashing a full Bitcoin block (128 rounds)[3] would take 1.49 days, for a hash rate of 0.67 hashes per day
