Thanks for pointing this out.
As bobble's answer already pointed out, this is detritus left over from earlier site reorganizations that shifted where the "meta" appears in the URLs. The old links should in fact work seamlessly, but the other possible issue is the original links on that page were all http://... instead of secure pages - and some browsers may have an issue with all the redirecting going on to take you to a secure page, for the updated "meta" URLs, and with whatever other canonicalization happens to URLs along the way. So, harmless, but annoying, and certainly unnecessary.
I've gone ahead and updated all the URLs on that Help page, making them https://... and using puzzling.meta.* instead of meta.puzzling.*