It's true, though, right?

Where does our responsibility lie in determining whether something is legitimate or not? There are cases where it's obvious, and cases where it's not. What's the limit of due diligence for a casual reader?

There's no reason whatsoever to think it's legitimate. Whatever the limit of due diligence might be, this isn't even close.

It's available and it hasn't been taken down, that's some indication it might be legitimate.

I agree that it's unlikely. But it's possible, and certainly much more ambiguous than grabbing a torrent off some ad-laden site for a TV show you can buy on iTunes.