> When I ask Google “Who did IBM’s Deep Blue system defeat?” and it gives me an infobox with the answer “Kasparov” in big letters, it has correctly understood my question. Of course this understanding is limited. If I follow up my question to Google with “When?”, it gives me the dictionary definition of “when” — it doesn’t interpret my question as part of a dialogue.

Google Search doesn't, but Google Assistant does. I posed the exact queries suggested by the article and the second query of simply the word "when" did give the correct answer (May 11 1997).