If I'm not missing something, before logging-in (registering) to Facebook, you was able to see that person's profile photo only and no other data or details. Am I right.
Situation, you're describing may be possibly coming from the fact, that anyone's Facebook profile photo is always public, no matter what. So, the person, that invited you to Facebook may set it's account settings, that everything (including entire page) is visible only to its friends. This way, you see his or her photo, when you're logged-off Facebook and see completely nothing, when you're logged-in (unless you accept or send and have accepted your Friends Request to that person).
This is a little bit strange, but not impossible in Facebook.
As for your second part. Yes, this could be an effect of someone's invitation without awareness. When you add a large number of e-mails to Facebook Friends Finder (either by uploading list from file or giving Facebook's access to your mailbox) it prepares list of all e-mails in your list that has Facebook account connected to it. It then presents you this with a checkboxesand allows you to uncheck some.
But... answer yourself, would you care for something like that? Most people just pass by to the next step, sending invitations to anyone from their e-mails list, that has Facebook account. This is a little bit tricky (or even stupid), especially, when you take a strong false-friends Facebook politics (if too many people click that they don't know you, upon your Friends Request, you may be blocked from sending these requests, have to verify your personality or even have your entire account blocked).
But the reality is, that it works like it works and both Facebook and the entire Internet are every day simply bloated with false-friends invitation without awareness.