In the article, he jumps off the from the insights from an older pre-web paper on information seeking behavior: The design of browsing and berrypicking techniques for the online search interface by Marcia Bates.
Here is a brief excerpt from the original article:
So throughout the process of information retrieval evaluation under the the classic model, the query is treated as a single unitary, one-time conception of the problem. Though this assumption is useful for simplifying IR system research, real-life searches frequently do not work this way... At each stage they are not just modifying the search terms used in order to get a better match for a single query. Rather the query itself (as well as the search terms used) is continually shifting, in part or whole. This type of search is here called an evolving search.Another reminder that search is an inherently interactive process and classical models that do not account for this are very limiting. On a related note, see previous coverage of Nick Belkin's ECIR 2008 keynote address (and Daniel's notes).