Since Hurley had never met Richard before Dr. Linus, it is unknown. It is possible that somebody told Hurley about Richard off camera.
Its possible Hurley was 'following' Jacob (which we couldn't see) as Jacob ensured Richard and Jack met up. Jacob may have told Hurley to ask about it (although this seems a stretch in many ways)
All of these are viable, but honestly the first thing that I thought was that the producers made a real error. It seemed pretty weak to me.