One other thing about the odd stuff... I joined "here" using my Yahoo WEBmail address, but as that had intermittent outages I switched my "membership"? email address "globally"? here to what you see now.
I see no change of address for you in GMF's Activity logs, so perhaps you changed your address before joining this group on March 12th. In any case, yes, if you changed your address on your Account page that changes it for all of your Groups.io subscriptions.