No, workerd and its semantics are not exclusive to Cloudflare infrastructure. People really do run it in production without using Cloudflare at all (I really wish I was allowed to say who because one of the users is hilariously ironic...).
Ryan's and Bert's core focus at Cloudflare is going to be making the self-hosting story better.
This was emphasized in the blog post: https://blog.cloudflare.com/deno-joins-cloudflare/