This forum is hosted by Discourse. Not surprisingly, it’s running through Cloudflare’s services, but you’re going to see some resources coming from outside of Cloudflare.
To answer your original question, Cloudflare is its own CDN and can cache some of your files. But only as a Pull CDN and not a Push CDN. It does not require a CDN subdomain, as your entire domain is already going through Cloudflare’s servers.