I will do:
While the rule may have been properly enforced, I would say that it's not properly phrased. But since I'm not a native English speaker, I may be wrong.
Whether this is a rule or a suggestion/advice isn't clear. It depends on context. To give an example: If a police officer in uniform 
tells me "this venue is not a good place to eat something", then I might interpret this as "I must put my food away or I'll be fined or get into trouble". But this actually depends on the country / jurisdiction. And perhaps it's no hard rule but just a suggestion. Maybe the officer just wants to warn me of birds (or trolls!? 
), who would attack me if I openly show my food. The police officer would act better if they told me: "Eating is not allowed here, but you may go over there, it's a nicer place to eat". Same polite, but clear regarding interpretation.
Now the problem with the pinned post is: there is no police badge err… moderator badge 
and the wording is open to interpretation, especially for non-English speakers, and may strongly depend on cultural background of the recipient. In some cultures, an "advice" can be interpreted as strict order, while in other cultures people take things more literally or say things more directly. (The latter can appear quite impolite to people who expect the former. I'm living in Berlin 
.)
I'll admit, this second part of the paragraph reads more like a rule (but still misses the police badge, figuratively speaking). Also, as the second sentence in the paragraph, it is in context of the "weak" phrasing that preceeds it.
Please don't get me wrong, I don't want to be nitpicking saying that this is not a rule. Especially after @notriddle's clarification below, it is clear that this is meant to be a hard or "proper" rule. I merely want to say that such phrasing leaves unnecessarily room for interpretation (apart from the place where it's posted which could/should be improved).
I think it's possible to be precise and polite. I would suggest trying to be both.
In my opinion, speculation of users whether some content of other users violates the rules will create a less polite atmosphere for everyone in the end. But other people may have different views.
Of course, we can't know what you talk about in private 
. But thanks for commuicating it now.
I would like to add a comment regarding this:
This really surprised me. It might be wise to add a note just below the submit button akin to what Wikipedia does:
(from Wikipedia)
By publishing changes, you agree to the Terms of Use, and you irrevocably agree to release your contribution under the CC BY-SA 3.0 License and the GFDL. You agree that a hyperlink or URL is sufficient attribution under the Creative Commons license.
(This cited text is not a contribution under the MIT or Apache 2.0 license. Do I have to write this now every time I cite something!? I'm not a lawyer 
.)
Anyway, my point is: If posting in this forum means you automatically publish something under an MIT and Apache 2.0 license, this should be made clearly visible. Currently this important detail is "hidden" under hamburger menu âžž About or FAQ âžž Terms of Service âžž Section 3 (User Content License).
As there may be legal consequences arising from carelessly citing or otherwise posting content, I think this "legal detail" deserves a more prominent place.
(I know that dealing with legal issues is always a hassle and it makes coding much less fun than it could be.)