Agreed. This individual was in with the Guanacos at one point but was split off some time before the Guanacos left and has been on the 'World's Farm' paddock since.
At one point this animal's picture was used (erroneously) on the sign for the Guanacos, though.
Although the colouration is broadly similar, it's too dark overall for a wild-type Guanaco. There's something about the overall body shape as well, and the hair is a slightly different texture (and longer). When it used to be kept with 'proper' Guanaco the difference was more obvious: http://www.zoochat.com/1070/guanaco-herd-152712/ (actually, looking at that photo there are two that look a bit 'dodgy' as Guanacos - 2nd and 5th from left)