A file pile is an inside joke by the founders of the company in their previous job at the leader in social marketplaces.
In one of the major releases in October 2011, the search result page was being redesigned. An engineer wrapped a facepile in a div tag with an id of file-pile-text-container.
Robert continually shakes his head in disbelief that anyone would even be able to make such a ridiculous typo; however, Lu has been able to make this typo (robert is shaking his head somewhere).