Probably some super fuzzy thesaurus that will take your words, and create a weighted list of words that are similar to them and so some search matching going down the weighted lists.

Maybe also, they take those queries that needed lots of fuzziness to get to the answer, and track what people click to relate the fuzzy searches to actual results. Keep in mind, what you might think is a super unique "tip of tongue" question, across billions of searches, might not be that unique.

Building a search system to find things can be much more optimized than making an AI to return an answer, especially when you have humans in the loop that can tweak things based on analytics data.