That example will exclude any stories contain a link to facebook.com/AppStore as the fb.link value.
However, there are some nuances here. Stories will contain a maximum of 1 fb.link value. It is possible that multiple links will be included in a story, so in order to ensure you filter against all of these, you should filter against DataSift's Links augmentation targets, such as links.url.
The following CSDL will match any stories containing "iPhone" or "iPad" which do NOT contain the link "https://www.facebook.com/AppStore":
fb.content ANY "iphone, ipad" AND
NOT links.url IN "https://www.facebook.com/AppStore"