what are communities supposed to be, link groups?

Pretty much. Communities/subreddits/magazines/“whatever they are called on other platforms” are usually defined with the topic that’s relevant for it, not with people participating in it. There are fairly obvious exceptions like “ask <whoever>”, but the overwelming majority will be something like “horses” and you are expected to throw anything horse related there. The way they are named on Lemmy is a bit deceptive, though.

w3 disagrees with your expectations

I am not sure how their social guidelines are relevant for my statement about technical implementations of ActivityPub.
I’m even less sure on what Open Graph has to do with all of this. Do you add ogp tags to your email messages and expect whatever client renders it to process them somehow? Maybe I’m underinformed, but I’m fairly sure no email client processes these tags in any way.

If you want me to touch the social part of this, it’s probably even more confusing for me.
I never heard about “DNI” before reading this thread and your definition is far from the first thing that comes up when you look up these three letters.
Even equipped with this knowledge, reading your profile produces more questions than answers.
From that “DNI” field the only thing I can say for certain is that you don’t want to talk to people younger than 7. Maybe I have an idea on who “Libs” are, but considering other entries there I’m really not sure.
If that field is supposed to be “read this list, if you belong to one of these groups, don’t talk to me”, how am I supposed to act on it if I can’t even tell what these groups are?

The amount of confusion it generates makes me want to write it all off as a joke, but you seem to care about it, thus it only makes it more confusing.