Short answer, yes. The current commit includes the hash of its parent(s), so its own hash reflects the whole history, and one can not change the history without also changing the current hash. Just like a block contains the hash of the previous block.
That's a Merkle Tree. A blockchain is an application of a Merkle tree in which each node contains transaction data, and a majority of clients agree that the longest chain of blocks is the correct one.
Git also uses a Merkle-DAG, but it is not a blockchain.
But this ‘definition’ seems to needlessly tie the definition to the kind of data you are transmitting. And if that were the case, couldn’t a software diff be considered a kind of transaction?
