Since Castlevania is the name of the castle, Dracula was probably the one who named it (unless it appeared with a name already, which is another discussion maybe). Since Dracula wasn't too big on guests, and I doubt he applied for a builders permit, then only a few people would even know the name of the castle.
Another theory would be that Castlevania is just the title that villagers give to a mysterious and evil castle that appears in the woods overnight.