Facebook – Decision process of the Facebook Translations app

Facebook has access to all friendship-data on their site, even if you lock down the privacy settings. As an addition many users share their contact-book or even e-mails with Facebook. Most peoples have filled out their profile quite decent so it has data about your school, your employer, your current place, your interests and so on. Although Facebook states it does not use it, they can track all users (and even non-users) across many websites via the "like"-button which is transcluded directly from Facebook.

From this data it can calculate this friend requests.

You can only send event invitations to friends and group members, not to everyone that likes your page. However, you can post the event on your page, so that it will appear in the News Feed of people that like your page. The post will have a Join link for them to RSVP to the event. If you want more exposure than that there is also the option of purchasing a Facebook ad for the event, in which case numerous targeting options are available (including the ability to target only people that like your page, or friends of those people, or everyone within 50 miles of your city with a certain interest, etc.).