My understanding based off this answer is that parent 1 is the branch being merged into, and parent 2 is the branch being merged from. So in your case, parent 1 is A, and parent 2 is B. Since a cherry-pick is really applying the diff between two commits, you use -m 1 to apply only the changes from B (because the diff between A and C contains the changes from B). In your case, it probably doesn’t matter, since you have no commits between A and C.
So yes, -m 1 is what you want, and that is true even if there were extra commits between A and C.
If you want to make the new history look a little more like the original history, there’s another way to do this:
git cherry-pick B
git checkout Z
git merge --no-ff --no-commit B
git commit --author="Some Dev <someone@example.com>" --date="<commit C author date>"
(If needed, you can create a new branch for B before cherry-picking.)
This will retain the author information, should give you a history that looks like this:
B'
/ \
Z -- C'
/
A -- C -- D
\ /
B