Azzarello said flat out that 'her history was intact.'
This means that there have been outsiders on Paradise Island, that for a time it was open to the outside world where they shared their knowledge, and that Hippolyta is capable of and has spent considerable time viewing the outside world and learning from it.
So they aren't completely isolated.
In this current incarnation, we have no idea how they raised Diana, what they taught her about the outside world, why she left Paradise Island and on what terms (though it seemed it was on good terms considering how well she was treated in issue 2). We don't know if she was taught to hate men or not, if she volunteered to go/won a contest to go/rebelled and left, etc.
Did they gather information from the men they slept with on ships? Clearly, at least three times a century they leave the island, so where does it say they never leave it otherwise?
Right now, we just have no clue.