I don't recall carrying out any review tasks on The Workplace. Why is this occurring?
When somebody proposes an edit to your post, you receive a notification. If you click through and approve that edit, that counts as reviewing a suggested edit. So even if you don't have enough reputation to access the review queue, you can end up doing a review under specialized circumstances. The first time you do that, you get the badge.
I believe that Suggested Edits is the only review queue where this sort of thing can currently happen.