You may use Cloudflare Pages and Workers (whether in conjunction with a storage offering such as Cloudflare Workers KV and Durable Objects or not) to serve HTML content as well as non-HTML content (e.g., image files, audio files) other than video files.
The said limitation should apply however to their tranditional service with orange on whether it is B2 or not. I am not sure if being a Bandwidth Alliance partner makes a difference.
So the gray area comes from an exception being granted from R2 not specified in that linked page. R2, like B2 is part of Cloudflare's bandwidth alliance, so is the unwritten exception for R2 or for the bandwidth alliance?