Unfortunately, there isn't a pithy one line sentence that expresses gratitude, and asks for clarification in a polite manner without appearing to be curt or rude. That is the nature of emails. Tone is very hard to convey in words unless you resort to elaborate and seemingly long-winded phrases.
In BrEng it is the norm to first apologize and then use softening expressions such as: Sorry to bother you; I was wondering if you could; Would you mind verb+ing; I hope I'm not creating a fuss; etc.
The first request is really an apology. You are openly blaming yourself for your "incompetency". This type of polite request could backfire if your interlocutor feels like an idiot for not noticing the error himself (if there is any error involved). Then again, the person could simply reply with a "Oops! My bad/mistake I sent you the wrong link."
I'm sorry, perhaps I am mistaken, but the link you kindly shared doesn't appear to be relevant for my situation. Am I'm missing something?
The second request implies that you know the link must be pertinent but you don't know where to look or how to use that information.
Sorry for bothering you, but I wanted to thank you for the link and ask if you wouldn't mind explaining how it can be useful to me.
bib's approach is the only one that feels non-aggressive.