On this question's revisions (but I remember seeing it in other cases) the diff shows the same tag being both added and removed.
The tagging system automatically sorts tags based on how many times they're used. However, this is relatively new, so when a new edit is processed for an old post, the system sees the sort as a delete and re-insert because it is now in a new position.
Such edits do count for the Organizer badge, even though the actual tags are the same in the end.
Also of note: rollbacks do not consider tag order, and a rollback to a revision where the tags are in a different order will leave them in whatever order they were in when that revision was made. Another edit will then reorder them again.