LinkedIn accessing FB and email contacts

LinkedIn has just suggested I know my father through an email address I setup and tested once or twice several years ago using my Gmail account.

The address is used as the contact point for an enquiries button on a charity Web site - the actual address is obfuscated on the site and so the only way it could have leaked out is from my Gmail testing.

My father never uses the email account directly to send email and he's not on LinkedIn.