They'll attempt to find a mis-statement, a slip up of any kind that doesn't jive with any part of the rest of the picture / claim in question. They may look at the post for anything negative directed at a given person or the company, or slander generally (eg second line from end). Even if it's a stretch. From there it's a short hop to tossing around a few legal threats to end or substantially complicate the entire thing for most people on the other side.
You're right - I can't see anything that would possibly prejudice his case.
While it's typical for lawyers to instruct clients "don't say a word" - making it easier for them to control the narrative - in this instance, it's entirely unnecessary.
In other contexts, I'd go further and say it might even be risky to do so, given there are laws around deleting/preserving evidence when litigation is anticipated.
Here, though, it's just a fairly innocuous request for advice.