Your first node was moved to Perl News (because it is mostly a link to an external article, which has become close to the primary purpose of that section). Several hours later, when the second node appeared, somebody considered the first one as a duplicate of the second and somebody else considered the second as a duplicate of the first (one of whom probably should read up on how to use consideration). After you started this PMD thread (and very roughly around the time the duplicate got reaped) the first node got moved back to Meditations (it may have also been moved back and forth more times, but not that I noticed).

As for how the second node appeared hours later: The most likely way for that to happen is a browser reload (which probably wouldn't have produced a duplicate if the original node hadn't been moved). Note that browser reloads can happen rather surprisingly just because you used the "back" button (and either at some point told your browser to stop bothering you when it is about to rePOST in order to get back to a page that expired from its cache or you just dismissed the warning dialogue). Note that I have yet to use a browser that consistently avoids perversely declaring pages as "expired" so that they must be reloaded despite there being no reasonable justification for such a conclusion (even after investigating the twisted, conflicting cache control headers that are part of HTTP).

And, yes, it is pretty stupid of a web site to not detect and prevent such duplicates.