I believe they’ve made the point that it’s not chrome’s fault, but the site’s/user’s - images displayed on websites should be webp to benefit from optimizations for displaying images, but download links should be a different format. The error would be either the user downloading the images from the display instead of the download (including from sites that do not offer images for downloading purposes?), or the website not including separate versions for download where relevant.

I’m not necessarily sure if that’s a good take, but that’s my interpretation of what’s being said.