They specifically say they use Imgix's CDN for the images, which can be confirmed by looking at the response headers. Fastly is used for their actual website,

They specifically say they use Imgix's CDN for the images, which can be confirmed by looking at the response headers. Fastly is used for their actual website, judging by the ASN info. Meaning they wouldn't be serving petabytes of images from CloudFlare, just HTML/CSS/JS, which should be perfectly fine.