Yes, most likely. Rebase hides the fact the 2 changes happened separately, a merge would make it much easier to see the different avenues that may lead to the bug.
We purposefully try not to do rebases in my team for this reason.
In this case it would not, you can see the commits between tag A and tag B either way. He simply didn't bother checking, either that there was no bug after rebasing or that the commits he'd rebased onto hadn't been released yet.