I've seen this happen too. I'm actually under the impression that LinkedIn will log in to your email account if they can. They keep asking me to "confirm" an email address by giving them the password. Sorry, not gonna happen. I believe (without hard proof) that if Alice send Bob an email talking about Cindy, all three will be suggested as people they may know even if none of them have explicitly indicated such to LikedIn. Facebook apparently does some similar things, but LinkedIn is creepy in this regard. And remember, it could be that they didn't rifle through your email, but someone whose contacts include you. Oh, and I'm sure their "app" requires access to your phone contacts for the same reasons.
I'm actually under the impression that LinkedIn will log in to your email account if they can.
That seems the most likely scenario to me to explain the article. Maybe they try to log-in with your email and linkedin password on the chance that you used the same password for both services?
Then again, on gmail, this should trigger a "login on new device" warning and shouldn't be possible at all if two-factor-auth is active.
