Why is Model:SetPrimaryPartCFrame() doing this?

I am using Model:SetPrimaryPartCFrame to move a model, but however, When the command moves the model, all of the model's other parts are placed at the center of the primary part. How would I go about fixing this? Script:

local PositionNum = ((math.random(-160,160))/4)
local FruitID = math.random(1,1)
local Bool = script.Parent.IsReady.Value

while true do
    if FruitID == 1 then
        local fruity = game.ServerStorage.Fruit.Apple:Clone()
        fruity:SetPrimaryPartCFrame(CFrame.new(script.Parent.Position + Vector3.new(0,0,(PositionNum))))
        fruity.Parent = game.Workspace

    end
    wait(1)
    PositionNum = ((math.random(-160,160))/4)
end