It is an excellent question.
Whenever people go to a church or a restaurant or a library or a sportsground or to a meeting they seem to know what the right behaviour is and adopt it accordingly. Sometimes you see a sign saying "quiet please" in a library, but you don't see such a sign in a church. Partly its because social conventions have been ingrained into people, and partly its because people can assess a situation very quickly and fit in.
So it is true that "this type of content" has not been clearly defined. But why does that matter? I don't go to a meeting and ask what kind of language is appropriate.
HR is a forum where people can exchange information about home recording. There should not be a need to describe how the exchange should take place, just as you don't need to describe how to behave in church, or a meeting. What makes HR different?
So it's a good question, but one that doesn't need an answer.
Or, if it does need an answer, why? So that people don't step over the line and get banned? Why would they even need to get near a line? If people were to get banned, it would not be by accident or mischance. It would be because they knew they were crossing the line . . . just like getting kicked out of a library for shouting.