This “People Talking About This” will measure the user interaction on a page. This user interaction includes Likes on posts, Wall post written by a member, sharing content, RSVP to page’s events, mentioning page’s name somewhere on Facebook, tagging Page in a photo, and Check-ins in case the page is of some place.
This is a good feature and will motivate page owners and admins to keep the page updated with good and quality content in order to keep users active. Also this “People Talking About This” matters a lot as this is a public metric i.e. visible to everyone visiting that page.