There is no tag nor any other [commit] pointing to
That's not what the history shows.
git show HEAD - it'll show what the two parents of the merge are. It looks from your graph like one is the
c79dc19, and that's why it shows up in your history.
Most likely, either the branch really started at
c79dc19 (so that was already on master), or the branch was merged to master as a fast-forward when
c79dc19 was its head.
fe62 <=master <=HEAD
fe62 <- c79d <=master <=HEAD
checkout new branch
fe62 <- c79d <=master <=branch <=HEAD
amend (on branch) gives a new commit
0c81 which replaces
c79d on that branch but doesn't change
fe62 <- c79d <=master \- 0c81 <=branch <=HEAD