LOL how are you supposed to notice that the other alanons don't share? unless people have to don different coloured hats to designate themselves "aa" vs "al-anon" vs "supportive but not being affected in any way friend" you're not going to know why anyone is there!
I absolutely get why a group might want shares from AA members only. But if it is important enough warrant stopping non-aa-ers sharing AND that group is going to allow non-aa-ers in for support/whatever, and given that it's an anonymous fellowship so they will go round the table/circle and everyone will be given the chance to share, because the chair won't know why any particular person is there either
necessarily, then as a member of that group I would have suggested a little leaflet summarising the rules of this group for people who are attending but don't have a problem with alcohol themselves (non-conference literature!), or a 1 word sentence upon opening each open meeting. That way no-one shares inapropriately, and the aa-ers don't have to listen to stuff that they feel uncomfortable over.
What you have done isn't shameful or embarrassing or stupid or wrong, forgive yourself
. You didn't know, and now you do, fair enough, you can continue to go if you want to support him, and/or you can seek out an alanon meeting where you can share to your heart's delight about your feelings and thoughts, welcomed with open arms?