Facebook and instagram connected? Please help me!?

[kate]

I'm signed in to both instagram and Facebook on my iPad, but both using different email addresses. Nobody I know knows about my instagram account and I don't want them to, but I recently got an update that said 'your facebook friend has joined instagram', and they have started following me. There's no pictures of me so I don't know If they even know the account t is mine. My facebook and instagram aren't even connected, so I don't have a clue how they found it? And will they know its me, like will it have said my name anywhere? Please help if you know, thanks x