Comment by SeanBoocock

Or consider another scenario: your friend went to said restaurant and paid for something; read an article about the restaurant; viewed/interacted with an ad for the restaurant; liked a social media post for the restaurant; or was geo-tagged at or around the restaurant. Any of the above would be sufficient to associate your friend and the restaurant, and I'd wager targeting your social graph after you've interacted with a product/service would have a good ROI.