Note - Im not sure if this is allowed, I searched and there were quite a lot of old Forum Bug posts but if there is a new rule please correct me and I will close the topic.
So I was checking my notifications this morning and saw this.
The system sends notifications to all members of a group, like trustlevel 2, and moderators. The edit history shows a tl3 edited the post, whe a high level user makes edits, the forum system might sometimes reprocess all notifications for that post, including any group mentions