After reading the adalytics report, it sounds more like ads that were meant to be viewed mid-stream and (presumably) on YouTube content, only when clicked, were instead served on auto-play, looping and muted on third-party websites that donn meet the standards of the sold product.
So like you said, but it seems more that buyers thought their ads would run on certain locations and circumstances that ensured higher viewer interest, and instead were being charged for ads played off screen, behind other ads, and some even viewed by “declared bots”.