Its origins are in the documents of Vatican II. Even Catholics didn't use the term before then. If the Orthodox are using it's because they've stolen it from Catholicism.
Well, I guess "stolen" depends on whether it was taken from us against our will. So it's debatable.
Btw, the follow up question, if I state it as a question, is will that one time use of "ecclesial communities" be it, or the start of the phrase being used among EOs?