Changing issue from "confidential" to "visible" appears to unintentionally subscribe people to the issue.
I recently received two notifications about closed issues in witch I was neither a participant, @-mentioned, or subscribed.
I seem to have been subscribed to both #26242 (closed) and #26243 (closed) unintentionally, and my guess is it has something to do with the following system note:
@bkc has also reported this same issue.