git log question

[Stephen Berman <stephen.berman@gmx.net>]

I thought if I call `git log <commit> -1' on the current branch, it will
only show <commit> if it is in the current branch, but I just discovered
this is not so: I called it with master current and <commit> being one I
knew was only in emacs-26, but nevertheless it showed that commit.  The
same thing with `git log --branches=master <commit> -1' and `git log
--branches="master" <commit> -1' (I couldn't tell from the doc if the
branch name should be quoted, but it made no difference).  What's the
required incantation?  Thanks.

Steve Berman