There is also another option. Suppose, for a moment, that I've sent my friend an email and he/she has allowed LinkedIn access to their Google Contacts, even though I have not...there is no reason LinkedIn wouldn't still show me them as a contact to add, since they know the connection. They just know it from the other side.
Except LinkedIn very explicitly said that doesn't have to be the case, and the article shows examples of LinkedIn suggesting that the author invites non-users from his Gmail contacts to LinkedIn.
