On this question's revisions (but I remember seeing it in other cases) the diff shows the same tag being both added and removed.
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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.