

No a blockchain is a chain of blocks. Its an append only datastructure that provides a cryptographically verifiable history. Proof-of-work is what allows for public concensus in crypto currencies like bitcoin, where as git uses signed blocks to identify different chains.
Who says blockchains cant also form a DAG?
Its a blockchain because each block contains a digest of the previous block(s), which creates a tamper-evident chain of digests for all history.
Its just a type of blockchain, just like a subaru is a type of car.
You might have grown up thinking “all cars have 4 wheels”, but my subaru has a fifth wheel in the back and its still a car because having exactly 4 wheels it not the defining charcteristic of cars.