[SushiHippie]

This is from the same person that made sponsorblock https://sponsor.ajay.app/

This means that it's the community that sees sensational thumbnails and changes them to some other thumbnail. By default dearrow shows random thumbnails if no other were provided by the community. But you can disable this and show original thumbnails, but if there is a community submitted thumbnail it will show the community submitted one. I think for example the arte thumbnails won't get changed to other thumbnails as they are not sensational/clickbaity/mouth open.