I wish these authors would define exactly "which blockchain" they hate. https://en.wikipedia.org/wiki/Blockchain "A blockchain is a growing list of records, called blocks, that are securely linked together using cryptography." So, yeah, git and mercurial are "dangerous nonsense". But of course they're really talking about cryptocurrencies and smart contracts, right? So why not put that in the title?
The important thing is that the article is very clearly referencing the concept of a blockchain used as a permission-less DB, which Git clearly isn't. None of the arguments in the article apply to Git, and saying "Well, but Git is a block chain" would not make the article moot - the author at best needs to clarify that they are talking about a blockchain + consensus mechanism.
I'd also note that Git and Hg predate the first use of the term "Block chain" (2011, according to Merriam-Webster) by 6 years, and their design was in turn inspired by even older systems.
The Merkle tree or Hash tree data structure that underlies the design was invented in 1979, and also fits the definition of "block chain" on Wikipedia.