Can I create anonymous repositories for double-blind peer review via GitHub organizations?
The fact that you created the repository is visible under your account's activity, so anyone following your account can see it in their feed. This can also be seen later by viewing your activity by subscribing to your RSS Feed.
However, generally this should be a concern for anonymizing for peer review, since the requirements are usually much lower — authors can often be identified by preprints and similar means anyway if someone really wants to find out, and reviewers are expected not to go looking for this information.
But if you have a GitHub account with a lot of followers or want to prevent anyone from checking if your account created the repository, then your proposed method is not sufficient.