Someone with enough knowledge to make a claim that something is or isn't a blockchain would take the hint.

The point I'm making is the block I linked, that included his comment saying that Steem could have been around in the 1970s, contains a reference block_id which includes a hash of the previous block.

The first 4 bytes of the block_id is the hexadecimally encoded block number and the following data is a truncated hash of the block.

Blockchains are created and verified by "chaining" together a series of data blocks that include cryptographic hashes to the previous block. The "chains" between old blocks and new are mathematically strong crypto hashes. Any attempt for a single party in a decentralized ledger to change transaction data in an old block will fail because it breaks verification of the chain.