To the dating site? No. My user account is created via email.

You didn't link your account on the dating site to your facebook account, but maybe the girl did, so facebook knew that the girl was in touch with your dating account, and somehow they had access to your dating profile which includes your email, which they matched in their email database to get your facebook account.

FB likely buys, sells and aggregates graph data from numerous other social sites and applies deep learning in order to pre-stalk possible connections and make other suggestions for users' "convenience."

You don't even have to, all you have to do is visit both sites from the same browser, and they can use the ad-network cookies to track you.

If you did use Facebook Connect or authorize an FB app in anyway, that would probably be enough to generate a link somewhere.

In any event, men tend to be the pursuers on dating websites. It sounds a lot like bragplaining. Except normally females do it, and they're a lot likely to see you as creepy because numbers are lopsided in their favor.

Not saying you're creepy - but the reason dating websites are a time sink is everyone's ecstatic about telling their story - no one's interested in yours. Even if they were very humble, you'd be competing against 10's to 100's of pastes.