tl;dr OP accidentally left a survey unfinished for the client, this a dispute was made. OP completed survey, client was okay to pay, but OP hadn't logged hours with always-on webcam thus money was refunded to client.
Seems to me the client got the work for nearly free (gaming the system time only) - I see nothing in the article about UPWork requiring the client return work product as consequence of payment refusal.