Also, the Beta Cluster seems to be having server issues, and I don't have the technical rights there to try and test this anyway. Would someone else be able to help with trying to replicate the issue?

It seems like the page was created by Vigilantcosmicpenguin, and was marked as reviewed by NPP patroller Annh07. If those two facts are correct, then I am a bit confused why this is titled "Non-autopatrolled user can mark own article as reviewed". Are you saying that Vigilantcosmicpenguin was able to see the Page Curation toolbar and click the "mark as reviewed" button?

No, he's saying that Anh07 shouldn't have been able to mark the page as reviewed since it's Anh07's action that caused it to be in the queue in the first place.

This is probably a wontfix then. The idea that NPP reviewers can mark as reviewed drafts they move to mainspace is well-established, and probably happens many times a day. For example, AFC reviewers with the NPP perm.