You did, by making the repo public. You didn't make a release tarball public, you made git repository, designed for collaborating on code changes public. In this case, other users of github (including the general public) are exposed to a repository and all that entails. If you have no intention to let others do PRs, you don't need to host a public repository, you just need to host public tarballs of your source code.

> they do not have a right to open requests on my page any more than people have a “right” to comment on a blog post or a YouTube video.

Youtube videos are one-way consumption of media. Git repositories have the concept of merging, which is taking remote repository content and assimilating it with your repo (as you know), that's PRs. public repo = public/open PRs, because that's how a vcs works. You're not hosting a social media content on Github, you're hosting a public version control system, and you have the ability to make it private.

Youtube is hardly a good analogy, perhaps twitter or blue sky is, although even then it's consumed content, not collaboration. In that example though, what you all are proposing here is similar to tweeting but turning off the ability to get "noted" by the community. You have the right to say whatever you want (within the site's policy), but others also have the right to make community corrections (notes) so you won't mislead others.