Comment by deepfriedrice

It immediately stands out that that link is to a /wp-content URL. AKA wordpress. AKA PHP. AKA very recently vulnerable (and perhaps still)...

Whereas other links (e.g. the immediate next one to arxiv) seem unaffected.

edit: That was a red herring. It seems to redirect all .pdf links I try that don't point to a valid snapshot. Very interesting.