No, the sense had nothing to do with the content and everything to do with the context. Perfect grammar and writing style were never enough to get me to trust an anonymous forum post or unknown bloggers post for certain topics like health advice. Sloppy grammar and writing style were never a deterrent for me believing them for other kinds of topics like where to check on the HVAC system to find the sticker. I think the line could more accurately be described as the level of risk if it's wrong.

I dunno, I've read a lot of very well presented nonsense and some very useful insights that were barely readable. I think it's probably useful that people are being trained out of this bias (though of course that's in large part because LLMs do tend to exploit this bias).

For what reason would grammar influence whether something is true or not...

We have other signals now.

Before we would find an intriguing post on the internet from years ago, and you have to verify it with additional research--it's easy to skip that additional research.

With a LLM when you're skeptical you can interogate it. One thing we know for sure is LLMs are quick to admit mistakes were made when interrogated, comically so. A LLM might not always recognize its own mistake, but at least it is available for easy interogation, unlike the forum posts of old.

Manual research from reputable sources remains an option.