I agree, however I think that we could've raised the issue even without directly mentioning the developer or his repository, and could have discussed it without directly pointing at someone who did it.

Because that only derailed the discussion into whether he personally can or cannot do it (which he definitely can), instead of focusing on the best practices about commit messages in FOSS projects in general.

I also think that there's a pretty huge difference between offering someone advice directly when interacting with him, such as your example about unsafe food practices, and posting a meme post with his name to an entirely unrelated social network.

So, for your example, I think it's ok to either talk to the guy handing out food, to comment on his post about it. However, if you took a recording of him doing it, and posted it publicly to Facebook while mentioning him by name (and not even tagging him, so he isn't notified) - that's not a good way how to give meaningful feedback or critique.