This wasn't only a "scientific piece" -- his stated reason for writing the post was to make a comment on the MSM -- and certainly it wasn't targeted only at scientific readers.

Anyone (like me) who read the commentary about the media, and mostly skimmed over the exhaustive detail on why the experiment was broken, was reading primarily an opinion piece, and certainly tone matters in that context.

I don't agree that tone "only matters for rhetorical persuasion" in the first place (or perhaps I disagree with the idea that rhetorical persuasion isn't always playing a role in scientific writing) -- but that's a larger discussion.