Notably, Hurley comments on Richard's similiar appearance in the past and present; though he has never met Richard prior to this. (And he clearly doesn't know who Richard is when he appears in the jungle). It could be a glaring continuity error, or we could assume:
- Hurley picked up on Jack and Richard meeting in 1977, and assumed the latter time travelled.
- Jack simply told Hurley off-screen as they walked through the jungle.
- Kate, who had met Richard in 2004 before encountering him in 1977 during the events in which Ben was shot, referenced Richard's similiar appearance to the group in Dharmaville after she and Sawyer visited the Temple.
- Miles, having met Richard in 1954, and seen him from a distance in 1974, told Hurley about him.
- Juliet, fully aware of Richard not ageing, could have told Hurley and the others in the 1970s.
- Sawyer, based on this information, could have done the same. Would explain Sawyer's complete lack of surprise on meeting Richard in 2007.
Ultimately, the writers could have goofed - or I think we're just to assume Hurley somehow heard about Richard at some point when the latter met several of the survivors; and just sacrified the logic of this to have the humorous exchange of Hurley thinking Richard is a vampire or cyborg. (Similiar, to how Jin heard about Aaron off-screen from Kate).