"Blockchain" is generally used to refer to systems that either 1) use the sequence of blocks to model changes in custodianship or 2) (more generally) enforce a set of rules governing the correctness of a given block.
That is, a block in the bitcoin blockchain is valid not only if its hash matches what one would expect given the included transactions, but that those transactions adhere to the rules of bitcoin. (No double-spends, no dust transactions, etc).
While there are data structures in a git commit that must be present and/or follow a particular set of semantics, git does not enforce anything about the _contents_ of those commits.
Another key distinction: blockchains seek consensus, whereas divergent forks in git repos are by design.
EDIT: I should probably not distinguish too much between consensus and rule enforcement, as those two are obviously intertwined. :)
That is, a block in the bitcoin blockchain is valid not only if its hash matches what one would expect given the included transactions, but that those transactions adhere to the rules of bitcoin. (No double-spends, no dust transactions, etc).
While there are data structures in a git commit that must be present and/or follow a particular set of semantics, git does not enforce anything about the _contents_ of those commits.
Another key distinction: blockchains seek consensus, whereas divergent forks in git repos are by design.
EDIT: I should probably not distinguish too much between consensus and rule enforcement, as those two are obviously intertwined. :)