Enabling that avoidance is precisely the purpose for having the separate sections, and according to the rules as stated, there aren't exceptions.
Beyond that one post (and its mirrors at the top of the cordoned areas), I can not find further detail. I did find a long-ago post by @drscorpio referencing an FAQ for the overall forum, but following the link gave a page-could-not-be-found error, and a search for "FAQ" turned up only one post, and that irrelevant.
From what I've seen in practice, folks feel comfortable with poppers, alcohol, and marijuana in the general areas of the forum, and it seems to be that those drugs (which are legal, or at least tolerated, at least in many places) are exceptions.
Given the purpose of the rule in the first place, I'd say if it seems to you, as a person who knows people who are in recovery, that a post outside the cordoned area is a significant issue or risk for your friends, it's totally appropriate to report it and let a moderator move it. That certainly will harm no one.
That said, this reply is my opinion only, and I think a lot of us would appreciate it (I know I would) if RawTOP (though he's busy, I know) or a moderator could update the rules thread with a bit more detail about what is or is not allowed, vis a vis drug references.