Presumably those planted grapes are predestined to become raisins, with different growing and harvesting techniques than grapes used for other purposes, so it's not too unreasonable to refer to them by a name that encodes that info. Would be interested to hear from a raisin/grape farmer, though.
There are specific varieties of grape that are grown to be turned into varieties of raisins.
It's probably right next to the pasture where they raise grass-fed beef.