Yep, I find it to be a terrible proxy for the question, "Which parts of the HTTP request-response cycle interest you?" Please, please, please, if that is your question, just simply ask that question. It gives the interviewee the opportunity to steer the conversation in a useful direction (especially if the answer is "Well, I'm not really interested in the details of that, but let me tell you what I am interested in..." which would not be possible with the original question, without sounding rude).
The problem with the original question is that it masks your true question and makes it really difficult to understand what the discussion is about. If someone is used to answering questions succinctly, directly, and usefully (which are valuable traits in a productive engineering environment) then it's really difficult to formulate a clear answer on the spot, regardless of your depth of knowledge. The best response is probably the question, "Exactly which part are you interested in, and in relation to what kinds of problems?"