This is about commit comments, not commit messages.
This was definitely not obvious to me from their announcement and I wouldn't be surprised if others similarly misinterpret it.
> Note: This change does not impact regular review comments or other comments made directly on a pull request.
Root cause? I didn't even know commit comments were a thing that GitHub had! I assume it was much clearer to everyone that knew about them.
Me too. It wasn't a term or feature I was familiar with, and (incorrectly) assumed they were talking about commit messages.