Are you sure that’s Chrome and not a website which selects the format based on the client’s advertised capabilities? I know Facebook did that and it confused a lot of people when a .jpg wasn’t a JPEG.
I thought this might have been caused by a difference in whether image/webp is included in the Accept header on requests for web pages (not requests for images), since some people who run web sites prefer to serve different html to UAs that support and do not support webp rather than serving different image formats at the same URL. But when I looked at the Accept header Firefox sends for pages, it included image/webp. So I'm not sure what these sites are doing.
