Oh right, "social media"

came under scrutiny yesterday. It seems I have the etiquette wrong - or have I?
I don't "do" a lot of social media. Yes, I know I have the blog. I am on Twitter and yes, I have a small presence on Facebook. I don't post masses of photographs. I keep my circle of friends there small. I think of them as genuine friends. They are, I hope, the sort of people I might actually have "a cuppa" with rather than bare acquaintances or people I might not even recognise in the street. Fair enough?
I also belong to a group where there is a President and a Secretary and a Committee. It is their role to run the group, not mine.
Intending to be a polite sort of cat I wrote to the Secretary of the group when an opportunity for the group came up. I "cc'd" it to the President. The message about the opportunity was passed on to other people by them. All that seemed right and proper to me and, I assume, to them.
One person responded by saying I could have put an announcement on the FB page for the group, that this was the purpose of social media - that the intention was "many voices".  This person runs the FB page. She would have been aware I don't - for very good reasons - belong to it. I could not have posted a message there  but -  until yesterday - I could have read the messages there. It was an "open" group. It attracted people who did not belong to the group but were interested in the activities of the members. Not all of them can belong to the group. Some of them live in other places or are unable to get to the meetings for other reasons. It sometimes attracted people and they joined the group. 
Surely that is the point of social media? The person who claimed the intention of social media to be "many voices" seems to have suddenly cut off the sound. 
I don't know whether that is what she intended from the beginning or whether she is trying to "encourage" me to join the page. I see no point in making it a closed group. The activities were in no way confidential or secret. To the contrary, it would have been useful to advertise them to anyone who cared to search for them.
I am wondering whether I have done something wrong? Have I entirely misread the intention of social media? Am I supposed to open up my life to a group just so that other people I don't know can view it? Have I caused a problem for other people?
I hope not. I don't really think I have but I find it a curious reaction. It is at odds with the statements which were made about the purpose of social media and does not take into account the caution  with which many people wisely approach it. 
I am sorry if I am the cause of the door shutting on other people but can someone please tell me if I have the idea of "social media" wrong?