The same piece of text can be found in multiple places in the library. The search menu randomly picks one of these locations each time you hit search.

You can verify that the text was actually in the book that you searched for before you searched for it by remembering the exact location of the page (hex, wall, shelf, book and page number). You can go to this location at any point in time, in the browser version or the offline version on any machine and will find the text that you searched for.