It was completely a joke as mentioned in the article :) It's not actually a blockchain, just a very crude linear merkle tree. The point is that pets are appended into the blockchain, and if enough blocks get appended that don't mention your pet's birth hash, your pet is "dead" like tamagotchi. You can read it in the article in detail.

It was an absurd application of "blockchain" in order to have a demo app to try to run on AWS Lambda within some hours and it worked! :)