Just a theory, but could it be that all those friends have your email in their contact list, and when they've done a bulk import Facebook has remembered that connection so it can suggest them to you if you ever join (and vice versa)? The data isn't on your side, it's on there's.

Of course there's a whole other (worthy) debate about that, but it doesn't necessarily mean Facebook didn't delete the data you added.

That's a solid point. Thanks!