So he has a computer and can click.

In any case a paper should not rely on an ephemeral resource like internet links.

Have you ever tried to navigate to the errata corrige of computer science books? It's one single book, with one single link, and it's dead anyway.

I’m unconvinced the researchers acted irresponsibly. If anything, a Google-shortened link looks—at first glance—more reliable than a PDF hosted god knows where.

There are always dependencies in citations. Unless a paper comes with its citations embedded, splitting hairs between why one untrustworthy provider is more untrustworthy than another is silly.